The invention discloses a diesel engine and a valve mechanism with the valve early closing function of the diesel engine. The valve mechanism comprises a valve push rod, a plunger, a control module and a switching valve. The valve push rod and the plunger are matched to form a plunger cylinder. By the utilization of the displacement characteristic of the valve push rod relative to a cylinder cover, the control module is fixedly connected to the cylinder cover, the valve push rod and the control module are matched to form a mechanical sliding valve structure to control an oil inlet and an oil return port of the plunger cylinder to be closed or opened, and then the sliding valve structure is matched with the switching valve located between a pressure oil path and an oil inlet oil path of the control module to control the oil inlet time and the oil return time of the plunger cylinder. When an oil return oil path of a control system of the switching valve and an oil inlet oil path of a mechanical sliding valve are disconnected, a valve of the engine is normally closed; when the oil return oil path of the control system is connected with the oil return oil path of the mechanical sliding valve, the valve of the engine is closed in advance. Compared with the prior art, the structure and the control process of the valve mechanism are simple.