A method of phase-matching three-decoy-state quantum key distribution is proposed with a weak coherent state source. The relevant parameters such as count rate and bit error rate are estimated, and the statistical analysis method of Chernoff bound is used to analyze the transmission performance of the method under the condition of finite data length. The simulation results show that the maximum secure transmission distance of the phase-matching three-decoy-state quantum key distribution scheme can reach 521 km, which is very close to the theoretical limit of the phase-matching infinite-decoy-state protocol of 536 km. As the data length decreases, the transmission performance of the scheme is declined.Even if the data length drops to 107, its maximum secure transmission distance can still reach 502 km.