A variable displacement oil saving electronic control system is provided by the utility model, which comprises a power supply circuit, a sampling circuit, a SCM main control circuit and an executive circuit. The power supply circuit provides stable power supply for the system from a 12 V automotive battery jar through a 5V voltage-stabilizing chip; the SCM main control circuit adopts ATM 2051 of atmel to analyze hits, and sends corresponding command information according to results. The executive circuit chip adopts a chip of uln 2003 and a power tube to drive an electromagnetic valve so that in idle status of the automobile, through controlling connection and disconnection of the cylinder by the electromagnetic valve, the automobile is in oil-saving working status. The utility model provides an automatic control device in simple structure with cylinder closing function for multi-cylinder petrol motors so that little gasoline is consumed and the automobiles are in optimal oil-saving status when the automobiles are idle. Optimal oil servicing status is restored without impacting normal running of automobiles during normal operation. The utility model is able to save gasoline, reduce oil consumption and reduce environmental pollution resulting from automobile off-gas.