This paper firstly presents experimental study of humidity distribution in an environmental chamber at different inlet temperatures and humidity. Experiment results show that, under fixed inlet temperature condition, the uniformity of the relative humidity (RH) in the chamber is better when the inlet RH is higher. It is mainly because of the coupled heat and mass transfer occurred between water droplets and air. In practice, direct measurement of humidity distribution in a chamber is infeasible and CFD simulation is a possible way to predict the humidity distribution. However, the use of CFD tools for predicting humidity field is rarely reported. Boundary and initial mist conditions are critical to the accuracy and computation efficiency of CFD simulation. This study then presents a CFD simulation method of the humidity distribution inside chamber using FLUENT based on some assumptions and simplification. Moreover, droplet sizes were measured by laser diffraction analyzer. The simplified droplet size distribution is used as initial condition for CFD simulation. Experiment results and CFD simulation results are compared and it can be concluded that the CFD simulation method can achieve satisfactory accuracy with reasonable computation load.