The invention relates to an MG53 mutant which is a mutant having either one or two or more cysteines of 7 cysteines in an RING structural domain of an N end of MG53 mutated into non-polar amino acids. The MG53 mutant has a prevention/treatment effect and application in protection of hearts and treatment of heart diseases caused by cell death, and especially, the MG53 mutant prevents simultaneously associated insulin resistance, obesity, diabetes and other side effects caused by the MG53 while protecting the hearts.