Abstract: A method for improving fuel efficiency of a vehicle and an exclusive energy saving and emission reduction device thereof are provided. The key points of the technical solutions are as follows. An exhaust separation device is installed in a crankcase of an engine. An oil-gas separation technology is adopted to manufacture an oil-gas separator and a diffusion vortex chamber. According to an aerodynamic principle, the separation degree of the exhaust is improved through compression and high speed vortex in the energy saving device, in such a manner that engine oil vapor in the exhaust is separated from combustible mixed gases, and then sent to the engine via an air intake throttle. The present invention enables complete combustion of the fuel, so as to achieve effects of oil-saving and emission-reducing.