In order to study the reducing and reusing of petrochemical residual sludge and solve the technical problem of traditional anaerobic digestion, the contrast research was carried out between the mesophilic (30 degrees C) and thermophilic (60 degrees C) anaerobic digestion. The result showed that the efficiency of thermophilic digestion was twice as big as that of mesophilic digestion. When sludge dosage increased, the concentration of volatile fatty acid rose sharply and pH value decreased correspondingly. When the reaction became stable, the concentration of volatile fatty acid began to drop and the corresponding pH value began to rise gradually. At each sludge dosage, alkalinity dropped first and then increased with the reaction carried on. In a different sludge dosage, the fluctuation of pH, volatile fatty acid, and alkalinity under the thermophilic condition was less than that under the mesophilic condition by a different sludge dosage. Through the experiment of sludge digestions, the optimizing technical conditions are as follows: biochemical reaction of residual sludge input rate: 10%; retention time: 10 days at a high temperature of 60 degrees C by full agitation.