Abstract: In order to improve positioning accuracy of underground personnel, an underground fingerprint module positioning algorithm based on WiFi was proposed. The algorithm saves measured signal strength from sampling point and its location information to form fingerprint database. WiFi terminal compares real-timely measured signal strength from wireless access point with information in the fingerprint database by use of matching algorithm, and calculates location of terminal by use of Euclidean distance formula. The test results show that the algorithm can realize accurate underground positioning.