Abstract: In view of the problem that it is impossible to quantitatively analyze the waste rock mixing at the top， side and front of the ore drawing by sublevel caving without pillar， a similarity physical simulation experiment of in-situ replacement method was adopted to obtain the barren ore mixing amount in each part and find the key points of barren ore mixing in each part. 15 group of experiments were design by using Box-Behnken method in Design-Expert.The influence of the interaction among the sublevel height， the distance between roadways and the distance of ore collapse on the mixing of barren ore were systematically studied.A quadratic response surface model with mixed ore ratio as the response value was constructed.The optimal stope structural parameters were obtained by using the response surface analysis method.The optimization results were verified by in-situ substitution method.The results showed that:① The similarity physical simulation experiment of in-situ replacement method was carried out by using the original structural parameters of segmentation height， road spacing and ore collapse distribution spacing with the values of 12 m， 12 m and 3 m respectively.When the ore recovery rate was 80%， the mixing rates of front， side and top barren ores were 16.7%， 8.3% and 2.5% respectively， and the total mixing rate of ore was 27.5%.② Trough the analysis of response surface model， it was indicated that the segmentation height， route spacing and ore collapse step distance and their interactions all have significant effects on the ore mixing rate， the correlation coefficients fitted by the regression model were all close to 1， the predicted data of the equation were consistent with the actual data， and the optimized segmentation height， route spacing and ore collapse step distance were 16.59 m， 17.42 m and 4.02 m respectively.③ When the ore recovery rate was 80％，compared with the original structural parameters，it showed that the barren ore mixing rate on the front and both sides was reduced by 3.6% and 1.7% respectively， the barren ore mixing rate on the top was increased by 0.7%， and the total mixing rate was reduced by 4.6%，which indicated that the ore drawing effect was good.The above study results further indicated that the study approach that using in-situ replacement method to analyze the rule of waste rock mixing，and adopting response surface method to optimize the structural parameters has certain practicability and operability significance，and has certain reference value for the optimization of mine stope structural parameters.

Key words: caving mining method, loss dilution, waste rock mixed, structural parameter optimization, response surface method