The principle and methods on thermal/vacuum (T/V) testing of microwave humidity sounder (MWHS) on FY-3B satellite were described; correction algorithms on calibration errors were developed, and some main specifications of MWHS-3B, such as linearity, sensitivity and calibration precision, were obtained. The parameters derived from the T/V testing had been used in in-orbit data processing to produce brightness temperature products in FY-3B ground system.