Hi Gao Xiang,
The H_blank and V_blank values are used to calculate the H_toal and V_total respectively. When you decied the resolution of video stream, i.e., the hight, width, bits/pixel and frame rate are fixed. Consequently, the V_total could be get from 1/(frame rate). In the CX3 receiver configuration tool, you need to set the MIPI CSI clock value, data lane, H/V_active value according to the resolution you choose.
After that, the configuration tool will generate some necessary parameters in the right panel of this tool.
If you change H_blank and V_blank, it will lead to a different value of some other parameters, such as the range of PCLK.
Hope this will help you.