Abstract: Fengyun 3B meteorological satellite (FY-3B) is the second generation polar-orbiting meteorological satellite, which is launched on 5 Nov 2010. Microwave humidity sounder (MWHS) is one important sensor onboard FY-3B and begins to work since 11 Nov 2011. MWHS is a five-channel total power microwave radiometer, which has 3 channels operating at 183 GHz and two dual-polarized channels working at 150 GHz (window frequencies).For channels of 150 GHz and 183.31 GHz, the angle resolution is 1.1°, making the resolution 15 km at nadir pixel. One motor drives two separated reflectors for 5 channels, and the scanning period is 2.667 s. Main beams of the antenna scan over the observing swath (±53.35° from nadir, 2600 km) at a constant periodicity of 1.71 s. During each period, two-point calibration is performed to calibrate the receiver gain and noise.A quantitative evaluation on the stability of the MWHS post-launch performance is carried out, which indicates the MWHS onboard FY-3B is improved comparing with that on FY-3A. Case assessment shows the MWHS can provide typhoon information, including the procedure of generating, developing and weakening as well as the rainfall caused by typhoon. During typhoon Linfa, Chan-hom and Nangka in 2015, high quality data are achieved, and the typhoon eye areas are clearly monitored with the aid of FY-3B MWHS.For precipitation, the scattering at frequencies around 150 GHz (dual-polarized) and 183 GHz result in significant brightness temperature depressions. According to the distributions of brightness temperature differences of channel 1 minus channel 5, channel 1 minus channel 2, and channel 3 minus channel 5, the precipitation and rain detection can be derived using neural network method. These quantitative assessment may provide reference for application of MWHS observations.