In view of difficult judgment when a volleyball falls in the vicinity of the court side boundary and the shortcomings of the existing judgment technology, the invention provides a device which can perform real-time accurate judgment and displaying when a drop point of the volleyball is in the vicinity of the court side boundary by using the photoelectric technology and the computer technology, and a judgment method. A detection device for detecting the drop point of the volleyball is constructed by using a fast laser correlation sensor (comprising a laser emitter and a laser receiver), and the laser receiver sends a detection signal to an operation processor 1; and the operation processor 1 processes and judges the signal by using a judgment program and sends a judgment result to a wireless receiving and displaying system via a wireless signal, carries out operational processing on the received result information via certain judgment logics, and displays the judgment result by using a display to remind a chief umpire in a competition to carry out judgment and penalty.