The preliminary isolation and purification by protein chromatography of cathepsin L from silver carp dorsal muscle were studied. The influence of ammonium sulfate saturation， acid treatment and dialysis bag of molecular weight during preliminary isolation on the activity of cathepsin L were mainly studied， as well as the influence of different types of ion exchange column chromatography and ion exchange equilibrium buffer pH during purification process on protein chromatography purification results were studied. The results showed that the optimal salting out ammonium sulfate saturation range was 55%-90%， the optimal acid treatment condition was pH 3.0 and the heat treatment was at 40 ℃ for 10 min， the optimal molecular weight of dialysis bag was 7 000 u. As a result， 45 ku electrophoresis pure cathepsin L was obtained by combining weak anion exchange chromatography and molecular sieve chromatography and using 20 mmol/L， pH 6.0 phosphate buffer as the equilibrium buffer of weak anion column. Moreover， the purification fold was 487 and the recovery rate was 22 mg/1 000 g. This method has the advantages of simple operation and high recovery rate， which lays a good foundation for exploring the effective method of inhibiting the deterioration of surimi gel.