The invention provides a hydraulic variable valve device of an internal combustion engine. The hydraulic variable valve device comprises a cam, a housing, a bushing, a single-rod piston and a hydraulic piston, wherein the bushing, the single-rod piston and the hydraulic piston coaxially and axially move; a one-way variable throttle valve and a one-way valve are arranged inside the hydraulic piston from top to bottom; the single-rod piston and the hydraulic piston form a hydraulic cavity; in a moving process, along the cam, of the hydraulic piston, the hydraulic cavity is sealed or directly or indirectly communicates with an external low-pressure oil source; the pressure of the external low-pressure oil source and the original position of the bushing are regulated, so that the movement rule, in the hydraulic cavity, of hydraulic fluid can be changed, and therefore, variability of the valve is realized. The hydraulic variable valve device cancels a dear electro-hydraulic servo motor, can remarkably reduce cost on the basis of guaranteeing flexible and variable valve motion, and is beneficial for engineering application of the variable valve technology.