The utility model relates to an adjusting device for valve lift of a cylinder head of a gasoline engine. The adjusting device comprises a baseplate, a support base, a guide rail, two sliders, two first connecting arms, two second connecting arms, two displacement sensors and two valve ejector rods. The support base is fixed on the baseplate. Two ends of the guide rail are connected with two ends of the support seat through the first connecting arms and fastening screws respectively. The sliders are mounted on the guide rail and are in sliding fit with the guide rail. The valve ejector rods are in screw joint with the sliders. The lower ends of the valve ejector pins penetrate out of sliding grooves of the ejector rods. The displacement sensors are positioned right above the valve ejector rods respectively, and are connected with the sliders through second connecting arms and fastening screws. The adjusting device is applicable to adjustment and measurement of lifts of intake valves and exhaust valves of different types of engines with different valve angles and valve intervals.