The effect of quantum well (QW) number on performances of InGaN/GaN MQW LEDs has been investigated.It is observed that V-defects increase in density and averaged size with more periods of QWs, resulting in larger reverse-bias leakage current and lower emission efficiency of LEDs.CAFM measurements demonstrate that V-defects may preferentially capture carriers, subsequently enhance local current and nonradiative recombinations at associated TD lines.