A tracking system includes a first device and a second device. The second device comprises an optical module, an ultrasonic module and a processor. The optical module is configured to capture image data in a first detection field. The ultrasonic module is configured to collect ultrasonic data in a second detection field different from the first detection field. The processor is configured to determine a relative position of a target device relative to the tracking device in a third detection field according to the image data and the ultrasonic data. The third detection field is larger than the first detection field and larger than the second detection field.