Based on the transmission structure in the nacelle of tilt-rotor,a lateral-torsional coupling dynamic model and corresponding dynamic equations were built.The dynamic responses in the three flight types were obtained by solving the dynamic equations,then,the gear tooth dynamic loads and the lateral dynamic loads of each component were calculated.Based on the dynamic loads,this paper proposed a method of calculating tooth face dynamic friction wasted powers and bearing dynamic wasted powers,and the dynamic efficiency of the transmission.The dynamic efficiency of the transmission in the three flight types were calculated,and the transmission parameters on the impact of dynamic efficiency in the three flight types were analyzed,laying a foundation for design of highly efficient transmission of tilt-rotor.