According to the changes in nutrient property and germination index（GI） of compost consisted of spent mushroom substrate and cattle manure in different ratios, the best ratio between two agricultural wastes to fully decompose was revealed. The method of indoor culture was adopted, in which the air-dried, crushed spent mushroom substrate and cattle manure were mixed in 7 proportions of 10∶0, 9∶1, 7∶3, 5∶5, 3∶7, 1∶9 and 0∶10. Suitable moisture content（60%） and C/N ratio（25∶1） of compost were adjusted by（NH₄)₂ SO₄ solution. Subsequently, the microbial decomposition agent was inoculated into the compost, and the aerobic decomposition test for 90 days was conducted. During the composting, pH value, TOC, total nutrient content（N+P₂ O₅+K₂ O）, C/N ratio and GI were analyzed dynamically in order to evaluate the best ratio of spent mushroom substrate to cattle manure. The results showed that:after the aerobic decomposition of 90 days, the pH value, total TOC and C/N ratio of compost had different degrees of reduction, while the total N, P, total nutrient contents and GI value had different degrees of increase. After the decomposition process, the compost consisted of spent mushroom substrate to cattle manure in 7∶3, whose pH value was reduced from 6.94 to 5.83, TOC content and C/N ratio were decreased by 41.0% and 71.9%, T value was given the minimum value（0.28）, total N, P, K, total nutrient contents and GI value were increased by 109.9%, 163.0%,39.7%, 124.3% and 89.0%, respectively. This ratio was evaluated by the maturity indicators mentioned above, and its advantage was more obvious over the other ratios.