Abstract: The dynamic model of drive system with a face-gear in helicopter transmission was presented.The excitation analysis of rotor to drive system in the cruise and the hover condition was carried out,while the dynamic load coefficient response between face-gears and a pinion in two flight conditions was computed.In the fixed installation and the floating installation,amplitude variation study of dynamic load coefficient between face-gears and a pinion with change of the non-dimensional rotor excitation frequency was developed.It is theoretically and practically significant to the development of helicopter transmission with a face-gear drive in our country.