Adjusting and controlling relative humidity(RH) in packages is crucial to ensuring the quality of modified atmosphere packaging of fresh produce. A modified respiration-transpiration model was developed. The model was based on heat exchange and gases mass transport phenomena across the package, gases heat convection inside the package, and mass and heat balances accounting for the respiration and transpiration behavior of fresh produce. And then the predicting model of the RH in modified atmosphere packages was proposed. The testing system of the gas composition and RH-temperature in modified atmosphere packages was established. Fresh Lentinula edodes were packaged in different initial gas composition and sample mass, and stored for 40h at 10℃, 80% RH. The parameters of respiration model for Lentinula edodes were estimated, and the RH and temperature in packages were measured during storage. In general, the model predictions agreed well with the experimental data, except the model predictions were slightly high in the initial period. The effect of the initial gas composition on the RH in packages was notable. In modified atmosphere packages of lower oxygen and higher carbon dioxide, the ascending rate of RH was reduced, and the packages were saturated slowly during storage.