Abstract: Objective: To investigate the plasma concentration of 5-fluorouracil(5-Fu) and area under time curve(AUC) in FOLFOX6oxaliplatin,calcium folinate and 5-Fu scheme treating advanced colorectal cancer,analyze the correlations between AUC,and reducing the incidence of adverse reaction and improving the therapeutic effect.Methods: Forty advanced colorectal cancer patients treated with FOLFOX 6 scheme were randomly divided into the control group and observation group(20 cases each group).Two groups were treated with chemotherapy for two cycles based on body surface area(BSA) administration.The control group was treated with traditional administration mode during two cycles.The observation group was treated with 5-Fu by intravenous infusion for 18 to 30 h in the first cycle,and adjusted dosage of 5-Fu according to the AUC of 5-Fu in the second cycle.The adverse reactions and efficacy between two groups were compared after chemotherapy.Results: The differences of the incidence rates of leveⅠ to Ⅱ diarrhea,gastrointestinal reaction,mucositis and level Ⅲ to Ⅳ myelosuppression between two groups were statistically significant(P<0.05).The differences of the incidence rates of level Ⅰ to Ⅱ myelosuppression,hand-foot syndrome and level Ⅲ to Ⅳ diarrhea between two groups were not statistically significant(P>0.05).The total reaction rate of observation group(60.00%)was higher than the control group(25.00%)(P<0.05).Conclusions: Real-time monitoring the 5-Fu blood concentration in advanced colorectal cancer patients treated with FOLFOX6 chemotherapy and adjusting the dose of 5-Fu according to the AUC can effectively reduce the adverse reaction,and improve the therapeutic effect.