Offshore pile foundation anti-scouring device and mounting method thereof

The offshore pile foundation anti-scour device comprises a pile foundation, a turbulent flow energy dissipation mechanism and a riprap mechanism, the pile foundation is of a vertically-arranged rod-shaped structure, the lower end of the pile foundation is used for being fixedly connected with a seabed, the turbulent flow energy dissipation mechanism comprises an energy dissipation slope, and the energy dissipation slope is provided with a filling hole; the energy dissipation slope body is fixedly arranged on the seabed and arranged on the pile foundation in a sleeving mode through the filling hole, a filling space is formed between the filling hole and the pile foundation, and the side face of the energy dissipation slope body is a slope face. The riprapping mechanism comprises a buoyancy part, a connecting rod and a riprapping part, the buoyancy part is slidably connected with the pile foundation and can drive the riprapping mechanism to float upwards under the buoyancy effect, one end of the connecting rod