The bearings will directly affect the performance of helicopter transmission system whether they are in normal work or not. Lubrication is the essential element for the normal work of bearings. Under the condition of the bearing design and manufacture technique, material technique is becoming more and more advanced, and lubricant becomes “the fifth main part”, which has been got a wide-ranged agreement. One of the most critical factors to improve bearing life is lubricant. This paper analyzes lubrication type and mode, and the failure of helicopter transmission system roller bearing caused by improper lubrication. It further explains the importance of lubrication to the bearings. And how to select lubrication mode and lubricant to improve the bearing life is also summed up.