For the serious scuffing failure during the process of the delivery test of the high speed crown gear coupling used in a NGW type epicyclical gearbox,the oil mass distribution and oil supply method of coupling in the gearbox are analyzed with three-dimensional CFD software,and the cause of scuffing failure is found out and the shortcomings of the design of original oil supply system is explicated. Finally,the reliable solutions for subsequent failure treatment and some reference for the design of similar couplings are provided.