The invention provides a hydraulic variable valve lift mechanism of a valve spring free engine. The mechanism comprises a cam shaft, a stator and an air valve, wherein the cam shaft is arranged on therotor in a sleeving manner and can rotate around the stator; a piston and a piston spring are arranged in the stator, and the piston spring provides an upward spring force to the piston; the lower end of the piston rod is fixedly connected to a roller, and the lower end of the roller is fixedly connected to the air valve; a guide slot matched with the roller is formed between the inner wall of the cam shaft and the outer wall of the stator, and the guide slot is of a cam shape; by controlling the hydraulic force at the upper end of the piston, the moving distance of the piston relative to thestator can be changed, so that the variable maximum valve lift can be achieved. The air valve spring is cancelled, so that the higher charging efficiency can be achieved, and meanwhile, the mechanismis simple to control, and engineering application of the variable valve technology is facilitated.