Abstract: Objective: To further prove whether auditory cortex topdown efferent exists and observe its effect on outer hair cells （OHCs）. Methods: Distortion product otoacoustic emissions （DPOAEs） were measured before and after decerebration in 17 guinea pigs. Results: DPOAEs amplitude decreased significantly and rapidly after decerebration and remained at the lowest levels for 2,5,10 min. DPOAEs gradually recovered to the previous levels with time delay. Conclusion: It was further demonstrated that auditory cortex efferent really exists and controls OHCs and DPOAEs via medial olivocochlear system （MOCS）. The possible mechanism was discussed in the paper.