Abstract: In order to improve the detection performance of vertical linear array airborne sonar for underwater targets, this study employs the ray acoustic model to investigate how variations in the airborne sonar beam angle affect the detection range for underwater targets under different typical sound velocity profiles. First, a detection range model for airborne sonar is established based on the sonar equation. Second, typical environmental parameters and sound source directivity are configured. The influence of beam angle variation on sonar detection range is then simulated and analyzed with Bellhop ray-tracing program under five representative sound velocity profiles: (1) positive sound velocity gradient, (2) negative sound velocity gradient, and (3) uniform sound velocity gradient in the shallow sea; and (4) positive sound velocity gradient and (5) negative sound velocity gradient in the deep-sea mixed layer. Finally, the underlying physical mechanism is explained by analyzing sound ray transmission loss induced by beam steering, and the optimal beam deflection angle is derived using Snell’s law. The results show that, when detecting targets in the direct acoustic zone within a deep-sea negative sound velocity gradient layer, the optimal emission angle corresponds to the beam center ray being tangent to the sea surface; whereas under all other sound velocity profiles, the beam should be directed horizontally. These findings provide valuable guidance for the operational deployment of vertical linear array airborne sonar.