A universal energy-saving system for multiple working conditions includes an electronic control unit and an actuator. The electronic control unit is adapted to sample, process running information of a vehicle and an instruction of a driver, control on and off of a fuel injector, and adapted to drive the actuator to lock or release an exhaust valve after opening the exhaust valve, so as to realize working under multiple working conditions. The features include: fuel of the engine is cut off when gliding, the exhaust valve is constantly half open, the engine races with reduced pressure; the inlet valve opens and closes normally, an inlet manifold is vacuum, direction and braking are not affected. When needing to do work or brake, the engine switches to the normal working condition automatically. Even if a fuel saving system fails, only the fuel saving function is lost, whereas other functions are normal.