Provided are a microbial agent capable of making a side slope and bulkhead vegetation community free of artificial maintenance and a construction method thereof. The microbial agent is prepared through the steps of preparation of fermentation raw materials, smashing of the fermentation raw materials, liquefaction, sterilization, fermentation, desiccation and packaging, and desiccation and packaging are conducted on the raw materials which are subjected to fermentation. The microbial agent comprises various fungi such as paenibacillus sp., bacillus amyloliquefaciens, arthrobacter humicola, pseudomonas graminis, phanerochaete chrysosporium, trichoderma longibrachiatum, aspergillus niger, rhodotorula mucilaginosa, sporobolomyces and clitocybe geotropa. According to the microbial agent free of artificial maintenance for the side slope and bulkhead vegetation community, by means of a nutrient substance circulation theory of dry branches and fallen leaves, the microbial agent is added to a target vegetation community in one time, in situ degradation is conducted on the dry branches and fallen leaves to activate microorganisms, in an ecological system, a new system which has the functions of matter circulation, energy flow, soil fertility increase and vegetation community update and succession is formed among the dry branches and fallen leaves, soil and vegetation, therefore, artificial cultivation of the side slope and bulkhead vegetation community is not needed, and plants grow vigorously.