Objective To develop a method of removing harmful gas in air in room of laboratory animal.Methods Based on principle of removing ammonia in industry,a small-sized equipment was produced.Results Simulant experiment indicated,when both fresh air by fan and cycling air by the small-sized equipment were in turn at intervals of one hour,the concentration of ammonia was 12.02ppm in air of laboratory animal room.Conclusion The system can remove ammonia in the room to a certain extent.