The lateral jet significantly impacts the external flow field by generating complex shock interactions and affecting the aerodynamic characteristics of the aircraft. To investigate the aerodynamic effects of dual lateral jets under high pressure ratio conditions, a three-dimensional numerical simulation method based on the Reynolds-averaged Navier-Stokes (RANS) equations was developed. The accuracy of the simulation method is verified through single-jet experiments, followed by a comparative analysis of aerodynamic characteristics for different nozzle diameters using the double jet configuration. The results show that the interaction factor for the larger diameter decreases by over 5% compared to the smaller diameter at negative angles of attack. This indicates an adverse effect on the aircraft overload for the larger diameter. At negative angles of attack, the thrust line for the larger diameter is further offset towards the head, with a maximum difference of 2.0%, which reduces the stability of the aircraft. However, at positive angles of attack, the thrust line for the larger diameter is offset towards the tail, with a maximum difference of 0.98%. This slightly improves the stability of the aircraft. Through the flow analysis, it is found that the separation shock for the larger diameter moves forward compared to the smaller one, while the reattachment shock at downstream of the jet reaches the aircraft earlier. This research provides a reference for the configuration selection of lateral jet applied in high-speed aircraft design.