The preparation of dialkyl dithio amino formate includes: adding carbon disulfide to the mixture of sec-alkyl amine, water solution of sodium hydroxide, dichloro methane and ethanol solvent for reaction at 10-60 deg.c for 0.5-5 hr, further reaction at 50-100 deg.c for 1-12 hr, and separation of the product. The present invention has less material feeding time owing to the once addition of the rawmaterial but carbon disulfide, less post-treatment time owing to less dichloro methane adding amount and high conversion rate.