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In order to solve the problem that non-line-of-sight(NLOS) interference affects wireless signal transmission in complex underground environment of coal mines, an ultra wide band(UWB) personnel positioning system in coal mine is designed. The system uses asymmetric double-sided two-way ranging algorithm with return frame mechanism for ranging without clock synchronization, which ensures the ranging precision. The positioning area is divided by the area discrimination strategy and the area correction strategy, so that the tag can only communicate with the base station in the positioning area to achieve positioning, which avoids a large number of invalid frames in the positioning process and improves the positioning efficiency. The weighted least squares method and the unscented Kalman filter joint positioning algorithm are used to solve the tag position coordinates, which improves the positioning precision. A backup power supply is configured in the base station to ensure emergency power supply in case of power failure. Two communication modes, Ethernet and LoRa, are adopted. When the Ethernet is disconnected, the ranging data is transmitted in the LoRa mode, which ensures the emergency communication of the system. The test results show that the system has high dynamic and static positioning precision and strong anti-NLOS interference capability. When the base station is powered off or the Ethernet is disconnected, the system can realize emergency communication for a period of time.