For the problem of wheeled robots in shortage of positioning accuracy with the traditional method of dead reckoning while only using encoder, an improved method of dead reckoning was put forward. A new theory of dead reckoning model was established according to the speed of two coaxial wheels measured by encoder, to remove the external interference as much as possible and improve the positioning accuracy. As environment map and the starting point were known, the model was able to carry on the accurate tracking and positioning for the robots through encoder, and provided accurate location information for robot navigation. The experimental results show that the improved dead reckoning method has much higher positioning accuracy than the traditional method.