In consideration of high organic matter content in biogas slurry of pig farm, and long cycle, high cost, and difficult to remove of other treatment processing, a binary co-precipitation system comprising an aqueous calcium oxide solution and AlCl₃ was applied to remove organic pollutants of biogas slurry. The effects of precipitant ratio, dosage, reaction time, and initial pH of biogas slurry on the removal of organic matter were investigated. The results showed that the maximum removal rate of organic matter reached 93% when the co-precipitant volume ratio was 1:2.5, the dosage was 1:1 (volume ratio), and the reaction time was 60 min at pH 9. The XRD, FITR, and SEM analysis of the precipitates before and after the reaction demonstrated that the co-precipitant could flocculate and precipitate organic matter by charge attraction with negatively charged organic matter, and complexation with normal valence metal ions in the biogas slurry. The precipitation reaction was rapid and could completely remove organic matter, and had good industrial application prospects in farm wastewater treatment.