In order to investigate the acoustic oscillation characteristics of gas-liquid pintle rocket engine and provide a reference for later optimization designs, a LOX/GCH₄ pintle engine with rectangular combustor was manufactured. The Euler-Lagrange method was used to simulate the acoustic response produced by transverse velocity disturbance, and the effect of acoustic excitation frequency on the transient spray combustion process was studied before fire tests. Numerical results show that the adopted transverse velocity disturbance can produce the first-order transverse acoustic oscillation response with the same oscillation frequency in the combustion chamber. The response of spray combustion to acoustic excitation can be greatly affected by the relative size of the disturbance frequency and the combustor natural frequency of first-order transverse oscillation mode. When the disturbance frequency and the natural frequency are equal, the pressure and heat of reaction oscillate in phase with the velocity disturbance in the first half of combustor, and the significant increase of pressure oscillation amplitude also causes spray flame to swing synchronously. Meanwhile, there is a tendency to shift from diffusion combustion to premixed combustion in the combustor. Methane burns completely in the shorter distance and the combustor temperature tends to be uniform.