This paper proposed the trajectory algorithm with the minimum turning radius for the automatic parking system. The automatic parking system makes parking more convenient. The automatic parking system is an extension of parking assist system. Parking assist system mainly uses image processing or infrared and ultrasonic sensor to sense obstacles and parking assist system needs a much more parking space. In order to fill up this gap, the study attempts to improve part of trajectory algorithm by combining the minimum turning radius in order to substantially reduce the parking space into 1.43 times the length of the automobile.