Factors influenced direct sequencing of PCR (polymerase chain reaction) products were investigated in this paper. It showed that the specialization of PCR products played a key role in their sequencing reactions and only which could be sequenced directly. It also showed that the PCR reaction residues (including dNTP, primers,and metal ion) affected badly on the sequencing quality, so the purification of PCR products was necessary before sequencing. In addition,the optimum templates amount in sequencing reaction rose with the increasing of their DNA size in a certain range.