A shift algorithm of an automatic transmission is decided by the compromise between the performance and the fuel economy of the vehicle. But because in the traditional shia algorithm, throttle opening and vehicle speed are used to decide the shift points, the actual load of the vehicle is not exactly considered. In this paper, to consider the actual load, that is, the road grade and the vehicle acceleration, the longitudinal accelerometer is used to decide the shift points. As the result, the performance and the fuel economy of the vehicle which adapts the new shift algorithm are shown better than the traditional one.