Abstract In the early works of Dayton, Schram and Jaeckel, the hypothesis or the model of theory on the outgassing process of material in the Vacuum was given. So far, these conclusions have been accepted as the base for research on outgassing process.But it has already been found that the experimental results of outgassing rates of some non-crystal-line materials (for example, rubber, plastics etc.) are not in agreement with the above mentioned theories. In 1964, we suggested two theoretical models, i.e., "twofold over lapping diffusion" and "non-uniform concentration diffusion". We found that all the abnormal phenomena observed in the experiments can be thoroughly explained by these diffusion mechanisms.We have improved the method of experiment in outgassing rate measurement.