Abstract: Regular Cu-Ag core-shell nanowires with diameter of 60~70 nm were prepared by chemical reduction method. The preparation process was carried out using two steps and the obtained Cu-Ag NWs were used to detect the malachite green standard solution and its residues in tilapia based on SERS coupled with chemometrics. Ultraviolet absorption spectroscopy(UV-Vis)and Transmission electron microscope(TEM)spectras showed that the silver film on the surface of Cu NWs was uniformly coated and the Cu-Ag NWs were uniformly dispersed;SERS results showed that the characteristic peaks of malachite green were clear in the range of 400~1800 cm^-1. When the concentration of malachite green was 0~20 μg/kg,there was a good linear relationship between the intensity of characteristic peaks and the concentration of malachite green. The minimum detection concentration of malachite green standard solution and malachite green residues in tilapia were 0.5 μg/kg and 1.0 μg/kg,respectively;Partial least squares(PLS)model showed that the coeffificients of determination(R²)of the measured and predicted values were 0.967 and 0.95,the relative analysis errors(RPD)were 5.897 and 6.171,and the root mean square errors(RMSE)was 1.007、0.595,respectively,which indicated that the model had great prediction ability. The prepared Cu-Ag NWs substrate had high reinforcing ability and stability,as well as low manufacturing cost. The method is accurate,sensitive and rapid,therefore the parpared Cu-Ag NWs has a great potential in the detection of trace harmful substances in food.