Microwave radiometer imager is used for detecting cloud images in satellite for weather forecasting. Its mechanical scanning?component part is a bias parabolic reflector antenna with a large diameter, rotating at a low speed. Vibration amplitude is an important parameter of the microwave radiometer imager, overvibration will directly affect the satellite attitude control. It is proven that the vibration is mainly caused by dynamic unbalance. An insitu experiment for low speed dynamic balance of microwave radiometer imager is done. The results show that low speed dynamic balancing insitu is an effective method to reduce vibration of the microwave radiometer imager.