Abstract: Objective To find a method for improving the quality of coding for malignant tumors according to the International Classification of Diseases (ICD) and edplore the feasibility and necessity of such a method. Methods The author collected 26 922 tumor cases and analyzed the matches of the codes for the position of tumors (C code) and the modality of tumors (M code). On the basis of searching result, mistakes in the coding were identified and the causes for these errors explored. Results and Conclusion Altogether 5 329 mistakes occurred in relation to the arrangement of C code and M code for various and complicated reasons, accounting for 19.79% among the cohort of cases investigated. The present methodology for the coding needs to be improved and better alternatives are possible on the basis of current technology.