Abstract: Objective: To observe the effect of HCPT, L-OHP and their mechanism of action for combined chemotherapy on human colorectal cancer cell lines. Methods: Naked mice model for human colorectal cancer cell line was established, and HCPT, L-OHP, L-OHP+HCPT were then injected intomice's peritoneal cavity respectively. Apoptosis of cancer cells was measured by flow cytometry; elec-tron microscope observation cellular type and the apoptosis rate. Furthermore, two different flow cyto-metric methods were used to analyze the cycle specificity of apoptosis. Results: The results showed thatthe size of subcutaneous transplantation tumor on nude mice was significantly decreased in HCPT andHCPT+L-OHP group, compared to the pre-treatment or control group. Both the HCPT and HCPT+L-OHP group showed apoptosis in tumor mass, as compared with the HCPT and control group, and the apoptosis rate was obviously increased in HCPT+ L- OHP group (P<0.05). The L-OHP group mainly exhibited cell necrosis. In HCPT+ L-OHP group most apoptotic cells were observed in S phase of thecell cycle. Conclusion: HCPT+L-OHP is an effective therapy to human colorectal cancer cell line,which mechanism probably is L-OHP enhances the role of HCPT in induces the apoptosis of colorectal cancer. And there is a synergistic interaction in the two drugs in S phase of the cell cycle.