The invention discloses a hard rock tunnel construction method based on water power cutting. The hard rock tunnel construction method based on the water power cutting is characterized by constructing multiple tunnel sections from back to front along the longitudinal extending direction of a tunnel. When any one tunnel section is constructed, the process is as follows: 1, surrounding rock classification advanced detection; 2, construction parameter confirmation, wherein the confirmed construction parameters comprise cutting parameters of a water power cutting machine and split force of a hydraulic splitter; 3, current constructed tunnel section construction: constructing multiple cutting sections of the current constructed tunnel sections from back to front along the longitudinal extending direction of the tunnel, wherein when any one cutting section is constructed, the process is as follows: construction preparation, water power cutting, hydraulic splitting and rectangular cutting block outward transporting; 4, repeating steps one, two and three for many times until the construction process of the constructed hard rock tunnel is finished. The method provided by the invention is simple in steps, convenient to implement, lower in input cost, high in construction efficiency, good in construction effect, and can simply, conveniently and quickly finish the construction process of the hard rock tunnel.