The invention discloses an engine air distributing device variable in valve timing and lift range. The engine air distributing device comprises a cylinder cover, an air valve, a cam and a control mechanism. The air valve is arranged on the cylinder cover and driven by the cam to move. The cam is connected to the cylinder cover in a rotating mode in the mode that the cam can slide in the axial direction, the height of the protruding part of the cam varies gradually, and projections, in the axial direction of the cam, of the protruding part are not completely overlapped. The control mechanism is connected between the cam and the cylinder cover and used for driving the cam to slide in the axial direction and positioning the cam in the axial direction. Through improving the shape of the cam and the installing structure of the cam, the valve timing and lift range of the engine air valve can be adjusted at the same time without replacing the cam, and the engine air distributing device is simple in structure, good in operation stability and beneficial to lowering the cost.