The invention relates to a biological preparation, in particular to a Trichodrema spp. microbial agent and a preparation method thereof. The method comprises the following steps: the dried and crushed 8-9 edible fungus chaff according to parts by weight is mixed with 2-4 auxiliary material according to parts by weight, the acidity-alkalinity pH of the mixed raw material is adjusted to 5.0-6.5, then the Trichodrema spp. suspension with 5-10 percent of mass ratio with the mixed raw material is inoculated to the mixed raw material and cultured for 7-10 days at the temperature of 8-30 DEG C, and after the Trichodrema spp. is generated, the well cultured material is dried and crushed to obtain Trichodrema spp. microbial agent. The invention takes the treated edible fungus chaff as the raw material to produce the Trichodrema spp. microbial agent, fully utilizes the rest nutritious substance in the edible fungus chaff as well as the characteristics of loose and permeability of the fungus chaff, promotes the value in use of the fungus chaff of the edible fungus, and simultaneously reduces the production cost of the Trichodrema spp. microbial agent, the produced Trichodrema spp. is mainly chlamydospore, the multiplication capacity and the colonizing capacity of the Trichodrema spp. in the microbial agent are enhanced, the capability of resisting the unfavorable environmental conditions is also enhanced and the survival time of the Trichodrema spp. is prolonged.