The invention relates to the field of starters, and concretely relates to a complex fermentation inoculum for night soil, and a preparation method thereof. The complex fermentation inoculum for night soil comprises 30-80mass% of a beneficial inoculum and 20-70mass% of a nutritional additive, wherein the beneficial inoculum is composed of Bacillus subtilis, green non-sulfur bacteria, yeast, Lactobacillus acidophilus, Pseudomonas and Streptomyces. The complex fermentation inoculum for night soil is rich in Bacillus spp, actinomycete, lactic acid bacteria and other beneficial microbes, and all the beneficial microbes can grow and breed in different ranges, and reach the logarithmic phase within a short time, so the fermentation effect is fundamentally guaranteed, and the stink of the night soil is effectively expelled within a short time.