Abstract: Effect of O2、CO2 、headspace and their combination of low oxygen modified atmosphere packaging system on quality of fresh shiitake mushrooms was investigated using response surface methodology(RSM). Results showed that headspace had the greatest impact on quality of mushroom as PPO activity, crude protein and total sugar content had reached a highly significant level, and the interaction between headspace and O2 had also researched a significant level. While the impact influenced by headspace and CO2 was not significant. And the interaction between O2 and CO2 had significant effect on total sugar content and PPO activity, but the effect on crude protein content was not significant. And the optimum conditions obtained according to the regression analysis of those three factors were as follows. O2: 4.59%, CO2: 20.13%, headspace: 0.67. PPO activity, crude protein and total sugar contents in mushrooms in optimizing conditions were 5.00U, 0.54% and 52.08%. Key words：Shiitake mushroom; modified atmosphere; Quadratic rotation-orthogonal composite design; Response surface.