Using the method of double primer oligonucleotide-mediated mutagenesis, the high expression plasmid of TaqND236, a derivative of Taq DNA polymerase, was constructed. To determine the frameshift mutation frequency of the in vitro DNA synthesis, we constructed a Gapped-DNA system using the pFDPM118 (a mutant of pUC118 with a -1 frameshift mutation on the lacZ gene) as template. By calculating the ratio of blue and white colonies on the X-gal plate after transforming E. coli TG1, the frameshift mutation frequency of Taq and TaqND236 was measured. It was found that the replication fidelity of the deleted Taq-TaqND236 increased more than 10 folds.