In my country's air traffic control security surveillance, the control of surveillance accuracy is very important. In recent years, aviation unsafe incidents caused by "low, slow and small" aircraft have gradually increased, increasing the difficulty of airspace surveillance. In order to strengthen the orderly management of the airspace and increase the monitoring requirements for "low, slow and small" aircraft, a monitoring method is proposed that uses an external radiation source as the transmitter and only establishes a receiving station. The monitoring of "low, slow and small" aircraft in low-altitude airspace enables the monitoring accuracy to meet the monitoring requirements near the airport's take-off and landing route. By deriving the HDOP, the precision factor is obtained as an index to evaluate whether the monitoring method can achieve the monitoring accuracy, and the simulation results are carried out for different numbers of receiving stations, failures of receiving stations and different heights of receiving stations. The accuracy in all cases is less than the derived HDOP, which proves that this monitoring method can meet the needs of civil aviation for the monitoring accuracy of low-altitude airspace near the airport.