Abstract:FY-3D Vertical Atmospheric Sounding System (VASS) temperature and humidity profile products are evaluated using radiosonde observations and ERA5 reanalysis dataset in Sichuan Basin and Western Sichuan Plateau. The results show that relative to ERA5 data, the average bias of FY-3D/VASS temperature in different seasons is from -0.631 to 0.500℃ and from -2.230 to -1.234℃ respectively, and the root mean square error is from 2.117 to 3.222℃ and from 3.077 to 3.460℃ in the basin and the plateau area respectively. Vertically, the accuracy of temperature is low at 800-700 hPa in the basin area and gradually decreases as the height decreases in the plateau area. The average bias of FY-3D/VASS specific humidity relative to ERA5 data is generally negative, while the average bias in different seasons is from -0.775 to -0.525 g·kg-1 and from -1.096 to -0.347 g·kg-1 respectively, and the root mean square error is from 1.251 to 2.367 g·kg-1 and from 0.696 to 1.991 g·kg-1 at the basin and the plateau area respectively. The accuracy of specific humidity is relatively low at 700-600 hPa. In consideration of the small diurnal difference in the accuracy of FY-3D/VASS temperature and humidity, the average biases of the two groups of evaluations are properly added. As a result, the average biases of FY-3D/VASS temperature and specific humidity can be indirectly obtained based on the radiosonde observations. Relative to radiosonde observations, the average bias of FY-3D/VASS temperature in the basin area is relatively small and the average bias in the plateau area is lower by about 2.440℃. The average bias of FY-3D/VASS specific humidity in the basin and plateau area is lower by about 0.612 g·kg-1. The above-mentioned results are significant for improving the weather and climate application ability of FY-3D/VASS temperature and humidity profile products in Sichuan Basin and Western Sichuan Plateau.