I have Video_Codec_SDK_7.1.9,i run the NvEncoder,i only modified the rcMode to NV_ENC_PARAMS_RC_CBR.
now it’s ok.i use mediainfo open the dest h264’s VBR.why? i really need CBR.

Where are you seeing VBR displayed? I have not seen MediaInfo showing VBR/CBR. Can you please post a screenshot? You can send it to me via a private message if you prefer.