The invention discloses a hydraulic oscillator for directional drilling operation. The oscillator is composed of a power sub and a vibration sub, wherein the power sub comprises a power shell, a bearing, a rotating shaft, a blade, a connecting frame, a rotating cylinder and a piston, and the vibration sub comprises a sliding sleeve, a sliding shaft, a connecting sleeve and a disc spring. The oscillator has the advantages that the rotating cylinder structure is adopted to directly push the vibration sub to perform periodic reciprocating vibration, compared with a traditional driving mode utilizing hydraulic pressure changes, the oscillation frequency is slowed down, the oscillation amplitude and period are stabler, the influence of high-frequency vibration on an underground high-precision instrument is effectively avoided, the overall working stability of a drilling tool is guaranteed, in addition, a drilling fluid does not scour damageable parts of the hydraulic oscillator during use of the hydraulic oscillator, the damageable parts comprise a rolling wheel, the disc spring and the like, and the service life of the oscillator is effectively prolonged.