ObjectiveTo evaluate the direct economic loss due to surgical site infection(SSI) from a medical economics perspective, and provide basis for health administrative departments to make strategies.MethodsSSI in patients undergoing breast, stomach and colorectal operation between March 2008 and February 2010 were selected for 1∶1 casecontrol study, patients with SSI were as SSI group, without SSI during the same period were as control group, difference in medical expense and length of stay between two groups were compared, economic loss due to SSI was evaluated.ResultsA total of 1 523 operation cases were investigated, 75(4.92%) developed SSI. 69 effective pairings were obtained. Wilcoxon signed rank test revealed that difference in medical expense between two groups was statistically significant（Z=6.586，P＜0.001）， the median of average medical expense of SSI group was 6 828.60 yuan higher than control group, all kinds of medical expense in SSI group were all higher than control group; the median length of stay of SSI group was 10 days longer than that of control group （Z=5.939，P＜0.001）.ConclusionSSI can prolong hospitalization, increase medical expense, decrease bed turnover rate, and influence economic income and medical quality.