A wireless tire-pressure monitoring system for horizontal wheels of a straddle-type monorail vehicle comprises eight tire-pressure sensors, four relays and one system host, wherein every two tire-pressure sensors are connected with one relay; the four relays are connected with the system host; each horizontal wheel is equipped with one tire-pressure sensor; a monitoring module capable of working independently is arranged in each tire-pressure sensor and comprises a pressure sensor, a temperature sensor, an acceleration sensor, a power module, a microprogram control unit and a radio frequency unit module; the relays are responsible for receiving tire internal pressure data sent by the tire-pressure sensors and transmitting the data to the system host through RS485 buses for analysis and processing; the system host is responsible for collecting and analyzing the tire internal pressure data uploaded by the four relays and transmitting the collected, analyzed and processed data to a TCMS (train control management system) host through an independent RS485 interface. With adoption of the wireless tire-pressure monitoring system, the tire wear is reduced, the service life of each tire is prolonged, the operational and maintenance cost is saved, and the operational and maintenance efficiency is increased.