In deviated well drilling, drill stems will naturally be pressed close to the borehole wall on the bottom side owing to the gravity with static frictional resistance produced, which will further evolve into backing pressure and lead to toolface, lower ROP and reduced drilling footage in a single trip; if not timely moving about the pipe, sticking accident is likely occur and even more with well abandoned. Therefore, friction reduction and backing pressure relieving become important parts of safe drilling. The magnitude of friction is decided by the component force and static friction coefficient of drill strings weight in borehole trajectory normal direction. In sliding drilling, some ways such as adding lubricant into the mud or making a short tirp (for borehole dressing) were adopted to reduce the static friction coefficient for the purpose of reducing friction and relieving backing pressure. In term of the classical physics, the static friction is greater than sliding friction; therefore, backing pressure relieving can be achieved by transforming the static friction into slide friction. In this paper, the application effects are evaluated based on the cause analysis on the friction, the mechanism of hydraulic oscillator and its application in Sulige gasfiled and Yumen, Daqing as well as some other oilfields. And the matters of attention in the use of hydraulic oscillator are discussed through the field test in Ya K1-7 well of Yumen oilfield.