To observe the clinical curative effect of heat clearing and dampness expelling method in perioperative period to prevent urinary retention after anorectal surgery. Methods： Ninety anorectal patients who were diagnosed as damp-heat type were randomly divided into two groups. The 45 patients in control group were given intramuscular injection of 1mg of Neostigmine. The 45 patients in treatment group were treated with oral administration of modified Longdanxiegan decoction. The curative effects of the two groups were observed. Results： There were significant difference of the therapeutic effect between the treatment group and control group(P<0.05).Conclusion： Heat clearing and dampness expelling method in perioperative period could relieve urinary retention after anorectal surgery, which shows the great advantage of Traditional Chinese medicine.