The Weather Research and Forecasting (WRF) model is used to investigate the radiative impacts of upper tropospheric clouds on water vapor transport from the tropical troposphere to the lower stratosphere. A 6-year simulation is conducted at 50 km resolution, with the model domain covering 15ºS to 45ºN and 180ºW to 180ºE. It is shown that the WRF model reasonably reproduces the spatial distribution and seasonal variability of water vapor in the upper troposphere and lower stratosphere comparing to the Microwave Limb Sounder (MLS) observations. However, the model simulated water vapor is moister than the MLS data and the simulated “water vapor tape recorder” travels faster than the MLS observation in the tropical tropopause layer (TTL) and lower stratosphere. By turning off the radiative effects of upper tropospheric clouds, we find that the radiative effects of upper tropospheric clouds warm and moisten middle and lower troposphere, but cool and dehydrate the TTL and lower stratosphere. The enhanced vertical motion due to the radiative effect of upper tropospheric clouds contributes substantially to the mass transport in the TTL.