Aiming at the requirement of high detection rate of target signal in the airport apron, the traditional target detection method is analyzed, and a mode S signal detection method with increasing falling edge decision is proposed. Furthermore, Genetic Algorithm is utilized to combine the stations with good reception performance to improve the detection rate. Compared with the common mode S signal target detection method, the receiver combination based on the improved method can obtain higher system detection rate. It can meet the requirement that the target area can calculate the target position in a probability not less than 99.9% with only 9 receiving stations. The simulation results of three-dimensional electromagnetic propagation model verify the effectiveness of the conclusion.