The invention provides an engine valve mechanism. The engine valve mechanism comprises an intake valve and an exhaust valve of an engine, a camshaft provided with an intake cam and an exhaust cam, wherein the intake cam and the exhaust cam are rotated by the crankshaft of the engine so as to respectively open and close the intake valve and the exhaust valve; and a phase variable mechanism. The phase variable mechanism enables the rotation phase of the intake cam/exhaust cam to vary relative to the camshaft. The camshaft comprises an intake camshaft provided with the intake cam; and an exhaust camshaft provided with the exhaust cam. The intake camshaft and the exhaust camshaft are configured to move relative to each other in the rotation direction. The phase variable mechanism comprises a driven member rotated by the camshaft; a guiding member that is rotating along with the intake camshaft or the exhaust camshaft and is capable of moving relative to the driven member in both the rotation direction and the axis direction; a centrifugal weight configured between the driven member and the guiding member; and a pushing member for pushing the driven member and the guiding member to approach each other. The centrifugal weight is pushed to move under the pushing force of the pushing member against the centrifugal force. Therefore, the guiding member is driven to move relative to the driven member in both the rotation direction and the axis direction, so that the phase of the intake cam/exhaust cam relative to the camshaft in the rotation direction is changed.