The invention discloses a parking lot vehicle trajectory tracking method and system based on an ultrasonic time sequence. By means of the parking lot vehicle trajectory tracking method based on the ultrasonic time sequence, vehicle information and implementation path information can be timely and efficiently acquired; according to the acquisition method, ultrasonic detectors are used for collecting information, data are sent to a parking lot management server through a communication network, and the server allocates parking space and plans a route for a vehicle and gives light guide. The vehicle position is detected through the ultrasonic detectors, vehicle trajectory tracking and positioning are realized, the deployment, operation and maintenance cost of the system is reduced and popularization is facilitated.