Self-adaptive hydraulic variable valve timing system for an internal combustion diesel engine, comprising an electronic control unit, an oil pump, a pressure regulating reversing valve, an oil return tube, an oil line, an oil supply main tube, an oil supply branch tube, and a self-adaptive pushrod length changing assembly. When the engine's oil exceeds 70° C., and engine's rotational speed is greater than or equal to 1300 r/m, and engine's load is greater than or equal to 50%, the control unit is configured to send instructions to the pressure regulating reversing valve to switch oil flow direction towards the oil line which leads to the self-adaptive pushrod length changing assembly and thereby put the engine in an operating mode.