The invention relates to an auxiliary method used for clinical early diagnosis of gastrointestinal tumors. The method comprises the steps of (1) decorating the inner wall of a capillary column; (2) preparing polyethylene oxide sieving medium containing TBE (Tetra Bromo Ethane); (3) collecting blood samples; (4) extracting DNA of genome in the blood samples; (5) taking the DNA of the genome as an amplification template, respectively designing p53, k-ras, APC and C-myc gene target fragment amplification primers by adopting pp5 to obtain a p53 gene PCR (Polymerase Chain Reaction) amplification sample, a k-ras gene PCR amplification sample, an APC gene PCR amplification sample and a C-myc gene PCR amplification sample; (6) conducting denaturation or incision enzyme on the p53 gene PCR (Polymerase Chain Reaction) amplification sample, the k-ras gene PCR amplification sample, the APC gene PCR amplification sample or the C-myc gene PCR amplification sample; (7) conducting CE-SSCP or CE-RFLP detection on a DNA sample solution subjected to denaturation or enzyme digestion; and (8) calculating the sum of mutation rates of CE-SSCP detection or CE-RFLP detection, namely accumulating the mutation rates. According to the auxiliary method, the operation is simple, the reproducibility is good, and the effect of prewarning of diagnosis of gastrointestinal tumors is achieved.