The measurement-device-independent quantum key distribution (MDI-QKD) system can resist any attacks on the side channel of the single-photon detector. In order to further optimize the multi-party MDI-QKD protocol, this paper investigates the multi-party MDI-QKD protocol based on W states, and introduces the detector quality factor (ratio of dark count Y0 to detection efficiency ηd) as an analog parameter to simulate and analyze the factors influencing bit error rate and key generation rate. The simulation results show that the increase of any one among the three variables of channel-transmission loss, fiber-channel distance and detector quality factor enhances the bit error rate and reduces the key generation rate.