The invention provides a noise tester of an engine belt tightener. The noise tester comprises a sound-proof housing, a base, a sound level meter, a microphone, a stepping motor and an engine gear system, wherein a tightener to be detected is arranged in the engine gear system; the engine gear system and the microphone are arranged in the sound-proof housing; the microphone is close to the end surface of a belt pulley of the tightener to be detected; a data line of the microphone is connected to the sound level meter outside the sound-proof housing; a driving wheel of the engine gear system is connected with the stepping motor outside the sound-proof housing through a transmitting shaft; and the stepping motor and the sound-proof housing are arranged on the base. The noise tester is used for measuring the magnitude of noise generated when the tightener operates, therefore the installation difficulty when the tightener is tested can be reduced, and the test efficiency is improved; meanwhile the interference from other noises can be reduced, and the noise test result of the tightener is improved.