I don't know why this code gets a memory overflow error for datasets with more than 20k of data. if anybody knows, thank you for your help.

int nMax = (int)numFIDTo.Value;
            int nMin = (int)numFIDFrom.Value;
            IStepProgressor stepProg = ArcMap.Application.StatusBar.ProgressBar;
            stepProg.MinRange = 0;
            stepProg.MaxRange = nMax;
            stepProg.Position = 0;
            stepProg.Show();
            try
            {
                IMap map = ArcMap.Document.ActiveView.FocusMap;
                IFeatureLayer flCrater = ClsShare.GetLayerFromName(map, comboBox1.Text) as IFeatureLayer;
                bool isPolygon = check_isPokygon.Checked;
                FrmAddField frmAddField = new FrmAddField(flCrater);
                int field_R = frmAddField.AddField("local_R", esriFieldType.esriFieldTypeDouble, true);
                IFeatureClass fcCrater = flCrater.FeatureClass;
                if (fcCrater == null)
                {
                    MessageBox.Show("撞击坑图层要素为空！");
                }
                IGeoDataset geodataset = fcCrater as IGeoDataset;
                ISpatialReference spatialR_Crater = geodataset.SpatialReference;
                IGeographicCoordinateSystem geoSys = ClsShare.GetGeographicCoordinateSystem(spatialR_Crater);
                IFeatureCursor featureCursor = fcCrater.Update(null, false);
                IFeature feature = null;
                double dDiam = 0;
                double dR = 0;
                IClone polyClone;
                IPolyline polylineClone;
                while ((feature = featureCursor.NextFeature()) != null)
                {
                    if (feature.OID < nMin || feature.OID > nMax)
                        continue;
                    if (feature.ShapeCopy.IsEmpty) continue;
                  
                    IPolygon polygonSrc = feature.ShapeCopy as IPolygon;
                    IPolyline polylineSrc = new PolylineClass();
                    polylineSrc.SpatialReference = polygonSrc.SpatialReference;
                    ISegmentCollection segs = polylineSrc as ISegmentCollection;
                    segs.AddSegmentCollection(polygonSrc as ISegmentCollection);
                    IPoint ptCenter = ClsShare.GetCenter(polygonSrc as IGeometry);
                    // 将中心点首先投影到地里坐标系上
                    ptCenter.Project(geoSys);
                    // 创建局部投影坐标系
                    IProjectedCoordinateSystem prjLocal = ClsShare.CreateLocalProjectedCoordinateSystem(
                    geoSys, 0, 0, 1.0, 0, ptCenter.X, ptCenter.Y);

                    polyClone  = polylineSrc as IClone;
                    polylineClone = polyClone.Clone() as IPolyline;
                    polylineClone.Project(prjLocal);
                    if (polylineClone.IsEmpty) continue;

                    IGeometry geoPoly = polylineClone as IGeometry;

                    //!<得到圆的外包最长边作为圆直径
                    dDiam = 0.0;
                    if (isPolygon)
                    {
                        //!<如果是提取任意多边形的最长直径，则要取矩形框的对角线长度作为最长值
                        dDiam = Math.Sqrt(geoPoly.Envelope.Width * geoPoly.Envelope.Width + geoPoly.Envelope.Height * geoPoly.Envelope.Height);
                    }
                    else
                    {
                        dDiam = Math.Max(geoPoly.Envelope.Width, geoPoly.Envelope.Height);
                    }

                    dR = dDiam / 2.0;
                    feature.set_Value(field_R,dR);
                    featureCursor.UpdateFeature(feature);
                    stepProg.Step();

                    System.Runtime.InteropServices.Marshal.ReleaseComObject(feature);
                    System.Runtime.InteropServices.Marshal.ReleaseComObject(polygonSrc);
                    System.Runtime.InteropServices.Marshal.ReleaseComObject(polylineSrc);
                    System.Runtime.InteropServices.Marshal.ReleaseComObject(ptCenter);
                    System.Runtime.InteropServices.Marshal.ReleaseComObject(prjLocal);
                    System.Runtime.InteropServices.Marshal.ReleaseComObject(segs);
                    System.Runtime.InteropServices.Marshal.ReleaseComObject(geoPoly);
                }
                stepProg.Hide();
                MessageBox.Show("撞击坑更新完成");
                System.Runtime.InteropServices.Marshal.ReleaseComObject(featureCursor);
                System.GC.Collect();
                System.GC.WaitForPendingFinalizers();
            }
            catch (Exception ex)
            {
                MessageBox.Show(ex.Message+"");
            }