I installed QGIS, GRASS and GDAL by OSGeo4w package, and as I finish the installation, I want to use GRASS tool, I face this problem：
But I already installed GRASS and SAGA, how to make those tools in QGIS to be used？
You need to configure the GRASS and SAGA folders in QGIS. Follow these instructions from the QGIS documentation on Configuring external applications:
The processing framework can be extended using additional applications. Currently, SAGA, GRASS, OTB (Orfeo Toolbox) and R are supported, along with some other command-line applications that provide spatial data analysis functionalities. Algorithms relying on an external application are managed by their own algorithm provider.