A composite biological agent with ternary microorganism for composting process of agricultural waste is composed of a composite biological agent I, a composite biological agent II, and a composite biological agent III, which is characterized in that the composite biological agent I is composed of bacillus, actinomycetes, microzyme and lactobacillus, the composite biological agent II is composed of trichoderma, ergillus, penicillium and trametes versicolor, and the composite biological agent III is composed of photosynthetic bacterium, azotobacter, phosphorus bacteria, and silicate bacterium. 30-60% composite biological agent I, 30-60% composite biological agent II, 10-20% composite biological agent III are mixed or applied to the process of composting process of agricultural waste in phases. Each component ratio and recruitment of biological agents can be both properly adjusted with different dung materials and dung purpose, thereby achieving purpose of using microorganism resources efficiently and raising fermentation efficiency.