Due to the unique environment of the Controlled Ecological Life Support System (CELSS), the type and quantity of organic solid wastes produced during long-term space missions are fixed. However, these mixed materials do not meet the indicators of conventional composting, and the vacuum in CELSS limits bio-degradation due to a shortage of functional microbes. In order to explore the feasibility of the organic solid waste ratio of CELSS and its microbial enhancement effect, composting experiments were setup to compare the actual and optimized material ratios on composting and polluted gaseous emissions, and to investigate the enhancement of microbial inoculation. The results demonstrated that the actual material ratio can be used for composting, whose degradation degree of crude protein, soluble sugar, cellulose, hemicellulose and lignin was better than the optimized treatment. The actual material ratio can also reduce 26.1% of ammonia (NH3) and 66.8% of methane (CH4) emissions. They were attributed to the carbon source in the actual materials, which resulted in higher species abundance, uniformity, and dominance of the microbial community and a stronger overall utilization ability. Moreover, the inoculation of VT microbial agent can further increase the diversity of microorganisms and prolong the duration of high activity, which helps to strengthen the degradation of crude fat, cellulose and lignin, and reduced 50.7% of hydrogen sulfide (H2S) and 33.2% of nitrous oxide (N2O) emissions. Therefore, it is recommended that the aerobic composting technology in CELSS use the proportion of actual organic solid waste to match the material and add VT microbial agent.