ObjectiveTo compare the effects of topical application of Modified Sanhuang Powder （加味三黄散， MSP） combined with cold compression versus cold compression alone on swelling and pain after knee arthroscopy through a retrospective cohort study. MethodsMedical records of 134 patients with knee arthroscopy-induced knee swelling and pain were divided into non-exposure group （51 cases） and exposure group （83 cases） based on whether they used MSP for external application after surgery. The non-exposure group received simple cold compression therapy in addition to functional exercise and routine treatment after surgery， while the exposure group received topical MSP on the basis of what were given in the non-exposure group. The Visual Analog Scale （VAS） scores were compared between the two groups before and 7 days after treatment， and knee swelling measurements were taken before and 3， 5， and 7 days after treatment. The clinical effective rate was compared between the two groups. ResultsThe VAS scores in both groups were lower after treatment （P＜0.05）， and the exposure group had lower scores than the non-exposure group （P＜0.05）. On the 3rd， 5th， and 7th days of treatment， the scores on swelling at 2 cm above the superior pole of the patella， at the midline of the patella， and 5 cm below the inferior pole of the patella significantly decreased after treatment in both groups （P＜0.05）， and the exposure group had lower scores than the non-exposure group （P＜0.05）. The total clinical effective rate in the exposure group was 91.56% （76/83）， which was higher than 78.43% （40/51） in the non-exposure group （P＜0.05）. ConclusionTopical application of MSP combined with cold compression is effective in relieving postoperative swelling and pain after knee arthroscopy and is superior to cold compress alone.