Measurement-device-independent quantum key distribution is immune from all the detection attacks, thus when it is combined with the decoy state method, the final key is unconditional secure. In this paper, the performance of three-intensity decoy state measurement-device-independent quantum key distribution at an asymmetric channel transmittance efficiency is considered and compared with each other at the symmetric choice scenario. Simulation result shows that the key rate at the symmetric scenario can tolerate 62 dB channel loss, otherwise when the distance ratio changes, the tolerated channel loss will decrease to 37 dB and 19 dB. A method to choose the optimal intensity is proposed for asymmetric channel transmittance regardless of distance ratio, which can be easily adapted to practical experimental settings.