The invention discloses a vehicle energy saving system with double fuel tanks and double engine sets. The system comprises the fuel tanks, the double engine sets and two gearboxes. The fuel tanks comprise the first fuel tank for containing high-octane fuel and the second fuel tank for containing low-octane fuel. The double engine sets comprise the large-compression-ratio engine set and the small-compression-ratio engine set. The two gearboxes are the first gearbox and the second gearbox. The high-octane fuel is provided for the large-compression-ratio engine set by the first fuel tank, the low-octane fuel is provided for the small-compression-ratio engine set by the second fuel tank, the large-compression-ratio engine set is connected with the first gearbox through a clutch, and the small-compression-ratio engine set is connected with the second gearbox through a clutch. A solution superior to traditional vehicle burning can be given under different driving speed states of vehicles, the utilization rate of the fuel is increased, and the purposes of saving energy and reducing emissions and protecting the environment are well achieved.