Abstract: The characteristics analysis of diode detector of satellite-borne microwave radiometer has been described. In this paper, given a certain observation target, the retrieved brightness temperatures changed correspondingly with the different values of system Automatic Gain Control (AGC). By adjusting the system gain, a little change happened for detector working range. The variation caused by nonlinearity of diode can not be completely eliminated by using two-point calibration method. The brightness temperatures retrieved in this paper are in a wide range of 3～350K. The experimental results demonstrate that there is obvious nonlinearity for brightness temperatures between retrievals minus actual values and observing values, which can not be eliminated by using two-point calibration. So, in the process of working and real-time calibration, the system must be assured working in approximately linear working range with a certain AGC value as possible.