Abstract: The oxygen concentration in compost system is a very important factor which influences composting process. It determines the activity of micro-organism in the compost system and then influences the degradation rate of complex organic materials in the compost. The influence of oxygen concentration on cellulose decomposing function of a composite microbial system MC1 was investigated. In order to find out the oxygen dependence and influence of environment oxygen concentration on this composite microbial system under static submerged culture conditions, two groups of experiments were designed to research this influence during cellulose decomposition process. One group used different sealed ways, and the other group used different cylindrical containers (different depths and diameters). The results show that oxygen is an indispensable factor in cellulose decomposition process, and the optimum concentration of environment oxygen was within 0.01-0.02 mg/L during cellulose decomposition process. The special oxygen concentration has an important influence on cellulose decomposing function of this microbial system.