How do can I calculate biomass for some agriculture by using VV and VH polarisation SAR images? I know there are some correlation for HV RADARSAT-2 to get biomass for some agriculture like corn, wheat, soy bean. So, what about sentinel-1?
In most cases (except for some types of canonical targets) you can assume reciprocity, that is VH == HV. You can use the same algorithm you were using for RADARSAT-2. See: http://www.nrcan.gc.ca/earth-sciences/geomatics/satellite-imagery-air-photos/satellite-imagery-products/educational-resources/9537.
Since you have access to an additional polarization (VV), you can also look at polarization ratios. Depending on the polarizations available, there are also some empirical or semi-empirical models that relate radar backscatter to properties such as leaf area index (LAI) which are in turn correlated with biomass, see for instance the Water Cloud Model (http://www.sciencedirect.com/science/article/pii/0034425784900105).
