A hydrogen-oxygen gas generator used for vehicles comprises a cavity base and an upper cover. Following components are assembled in a sealed cavity, wherein a longitudinal partition plate used for dividing the base into two longitudinal cavities is arranged in the middle portion of the rectangular base in the longitudinal direction; multiple transverse partition plates connected with the two side walls of the base are arranged on the two side faces of the longitudinal partition plate at intervals; the two longitudinal cavities are divided into multiple small electrolysis chambers through the multiple transverse partition plates; a device for supplying water to the small chambers is arranged; a filter plate is arranged above the water supplying device; multiple gas holes are evenly distributed in the filter plate; a gas outlet hole is formed in the top of the upper cover; a hydrogen-oxygen gas connector is arranged on the top of a rotating cap; a high water level detection part, a lower water level detection part and a public electrode binding post are arranged; and a binding post via hole and a positive and negative electrode via hole which correspond each other are formed in one side of the upper cover. Hydrogen and oxygen which are generated by the generator and fuel oil in an engine cylinder can be combusted together, and therefore the combustion efficiency is improved, and the output power of the vehicles is improved; and emission is reduced.