The invention discloses an anaerobic biological treatment process for treating sewage, which belongs to the technical field of sewage treatment, and comprises the following steps: 1, introducing sewage into a pretreatment tank, and pretreating the sewage by adopting a macromolecular treatment agent; 2, introducing the pretreated sewage into an anaerobic tank, pre-placing a compound microbial agent in the anaerobic tank, adding a carbon source, and carrying out preliminary anaerobic treatment under ultrasonic and irradiation conditions; and step 3, removing irradiation, keeping the ultrasonic condition, and continuing anaerobic treatment to obtain discharge water reaching the standard. According to the invention, microorganisms are coated in the capsules to form the compound microbial agent, so that good conditions are provided for attachment and growth of the microorganisms, and the anaerobic treatment effect of the microorganisms on sewage is effectively promoted; kitchen waste and kitchen garbage are used as an external carbon source, so that waste recycling can be realized, and a new sludge problem which is difficult to treat cannot be caused; defects and defects in the prior art are improved, and the maximum effect of sewage treatment through a biological anaerobic technology is achieved.