A valve clearance adjusting structure for a four-valve motorcycle engine comprises a valve rocker driven by a cam at one end, a valve rod driven by the output end of the valve rocker, and a valve clearance adjusting pad arranged on the top of the valve rod, wherein the output end of the valve rocker drives the valve rod after directly contacting with the valve clearance adjusting pad. The valve clearance adjusting structure can smartly adjust the clearance between the rocker and the valve by using valve clearance adjusting pads with different thickness according to different valve clearance. The structure can cause the transmission structure of motorcycle engine to be simpler and compacter, reduce the transmission links according to the law of motion, and reduce elastic deformation and transmission error of the entire transmission mechanism. Since the output end of a valve rocker with better rigidity and strength is used for motion transmission with the valve, the rigidity of the entire transmission mechanism is improved greatly and the additional vibration load is reduced greatly, thus improving the rotation speed and the power, and facilitating power performance of the entire engine.