In the drilling process of horizontal well with three-dimensional trajectory of unconventional reservoirs, the drilling speed is seriously restricted by the backing pressure effect. Hydraulic oscillator can generate axial vibration to reduce the friction between string and hole and significantly reduce the backing pressure influence so as to achieve the fast drilling. This paper introduces the working principles and performance of AG-Itator hydraulic oscillator as well as the test application effects in a variety of areas of China. It is showed that by the application of AG-Itator hydraulic oscillator, ROP can be significantly increased with shortened drilling cycle, which is an effective method to increase drilling speed for horizontal well with three-dimensional trajectory of unconventional reservoirs and is worth popularization and application.