Aiming at the fact that the asymmetric channel is not considered in the traditional quantum key distribution (QKD) protocol, the performance parameters of measurement-device-independent QKD protocol for the asymmetric channel with heralded single-photon sources are investigated. The relationships between the mean-photon numbers, the unilateral transmission efficiency, the key generation rate and the channel transmission loss in the protocol are analyzed. The performances of measurement-device-independent QKD protocols with the heralded single-photon sources for symmetric and asymmetric channels are compared. The simulation results show that, as the channel transmission loss increases, the key generation rate and the safe transmission distance decrease gradually, but the performance for the asymmetric channel is still higher than that for the symmetric channel.