Abstract: Based on the distinguishing launch technology of trapped launch vehicle, a simplified launch jet noise test system is designed and developed. The test system can be used to simulate jet noise and jet flow field about liquid rocket launching with single nozzle. Then the series of launch jet noise tests are accomplished. The test results show that the height domain SPL curves of launch jet noise are different from that of free jet noise, while changes of SPL along with time among different test points show the similar tendency, which is caused by the launch pad disturbing. The frequency domain SPL curves indicate that there are wide frequency characteristics and distinct screams about the launch jet noise, and the screams of launch jet noise usually have harmonic multiple frequencies or monophonic frequency. The launch jet flow field tests accomplished with the launch jet noise tests show that the developing tendencies of time domain SPL curves of launch jet noise are also similar with that of the engine working pressure and the launch jet flow pressure.