Micro light emitting diode display (Micro-LED) has a wide range of application prospect as a new display technology and has been developed rapidly in recent years. However, as the size decreases, the luminous characteristics efficiency of Micro-LED decreases sharply, which is due to the influence of sidewall damage. In this paper, the Micro-LED mesa structures of different sizes were fabricated by photoetching and inductively coupled plasma (ICP) etching. The surface physical damage and enrichment of impurity elements caused by etching on Micro-LED were analyzed. Tetramethylammonium hydroxide (TMAH) was used to repair the sidewall damage and cathodoluminescence (CL) was used to characterize the optical properties. The results show that with the decrease of the size, the impact of sidewall damage becomes more serious. After passivation with TMAH, the sidewall can be effectively repaired and the luminescence intensity of Micro-LED can be effectively improved.