Inlet conditions, including inlet size and location as well as inlet temperature and humidity, have significant effects on the humidity distribution in building room, testing chamber and built environment. This paper presented the investigation of the changes of inlet air temperature, humidity and inlet vent positions on the humidity distribution in the environmental chamber through experimental approach and simulation method. The average relative humidity (RH) and humidity uniformity inside the chamber with different inlet vent positions were investigated. The results show that non-uniformity of the humidity distribution decreases with the increase of the inlet RH value under low inlet temperature conditions while it increases with the increase of the inlet RH value under high inlet temperature conditions. The humidity uniformity is not very good under the lower inlet vent positions. Comparison studies on the humidity uniformity between experimental tests and numerical simulations show that the simulation results agree well with the experimental test results.