The optimal condition of pretreatment of biogas slurry by coagulation was researched in order to provide reference for the pretreatment of biogas slurry. The effects of coagulant tcchnique were evaluated according to the removal of COD, TN, TP, color and SS under laboratory conditions. The optimum technological conditions were determined based on the single factor and orthogonal experiments. The results showed that in the conditions of which dosage of PAC is 4 g/L, dosage of PAM is 50 mg/L,stirring speed is 200 r/min,while PAC and PAM are added in stage of coagulation, the contents of COD, TN, TP, color and SS were decreased to 216.20, 181.99, 0.18, 11.77 and 71.67 mg/L respectively, the removal rate of COD, TN, TP, color and SS were reached to 92.51%, 88.85%, 99.75%, 98.37% and 89.46% respectively,which could completely meet the discharge standard of pollutants for livestock and poultry breeding(GB18596-2001),which can reduce the load of subsequent wastewater treatment and provide theoretical support for the practical treatment of biogas slurry.