The invention discloses an engine valve structure. The engine valve structure mainly comprises a valve, a guide pipe sleeves the valve, a spring sleeves the periphery of the guide pipe, a spring seat is arranged at the top end of the valve, a lock piece is arranged in the spring seat, and a valve oil seal is arranged between the spring seat and the spring. The engine valve structure has the advantages that by the aid of the variable-pitch valve spring, close fit between the valve and a valve seat or a valve seat ring when the valve is closed can be guaranteed, inertia force generated by a valve mechanism when the valve is opened can be overcome, and a drive part is always controlled by a cam and is not separated from the cam; since inherent frequency of the variable-pitch spring is not a constant value, sympathetic vibration can be avoided and normal working of the valve is ensured.