The double rear axle driving system of tow tractor of SGA92150 mine semitrailer is developed on the base of the chassis of SGA3722 mine truck.A special power transfer case,one of the key facilities for the double rear axle driving system was designed.Through analyzing the principle and function of the double rear axle driving system,the paper expounds the design scheme of the power transfer case and the characteristics of its whole structure in terms of the condition of power distribution,chassis structure,transfer torque and driving mode.The developed power transfer case has made satisfactory result in practical engineering application.