The invention relates to a treatment method of organic solid waste. The treatment method comprises the following steps of: homogenizing the organic solid waste and then preheating, carrying out a thermal hydrolysis reaction on the preheated organic solid waste, then pushing the material into a depressurization tank and a buffer tank to be subjected to primary depressurization and secondary depressurization and then temporary storage, then carrying out heat exchange on the material, carrying out anaerobic digestion on the material subjected to heat exchange, carrying out vacuum degassing treatment on digested sludge in a digested sludge tank, dehydrating the treated digested sludge to form dehydrated sludge, conveying the dehydrated sludge to a drying room to be dried, and producing dried biogas residue. According to the treatment method of the organic solid waste, high temperature hydrolysis and anaerobic digestion technologies are adopted, the problems that resource is wasted when a burning method is adopted and secondary pollution can be easily caused when a burying method is adopted can be avoided, digestive efficiency in follow-up anaerobic digestion is improved, standing time of an anaerobic digestion process is also reduced, and sludge subjected to anaerobic digestion is subjected to vacuum degassing, so that carbon dioxide and ammonium nitrogen in the digested sludge can be effectively removed, and sludge dehydration efficiency is improved.