The invention relates to a hydraulic downhole half-stroke rotating clutch, which comprises an upper shell, a spline shaft, a spring, a bearing, a lower shell and a ratchet mechanism, wherein the upper shell and the lower shell are connected to form rotating fit; the spline shaft is a hollow structure which penetrates through the internal parts of the upper shell and the lower shell; an spline shaft upper spline, a moving ratchet, a spline shaft ratchet and a spline shaft lower spline are arranged on the outer wall of the spline shaft from top to bottom; the spline shaft upper spline is matched with an upper shell spline and the spline shaft lower spline is matched with a lower shell spline; the moving ratchet, the spline shaft ratchet and a fixed ratchet form a rotating fit ratchet mechanism; the spring is installed between the spline shaft and the lower shell. The hydraulic downhole half-stroke rotating clutch provided by the invention has the advantages that the structure is simple, the clutch is convenient to operate, the installation is facilitated, the safety and the reliability are high, the mutual conversion between a sliding drilling method and a combined drilling method can be realized without making a trip, a drill stem can be rotated during sliding drilling and the goals of improving the steering drilling efficiency, reducing the drilling cost and improving the well bore quality are achieved.