Abstract: Hardness is one of the important quality characteristics of nutrition bars with a significant effect on the purchasing desire of consumers. Previous studies have shown that the hardening of nutrition bar during storage is a common phenomenon caused by physical changes and chemical reactions,and many factors can affect the hardness changes. This paper mainly discusses the effects and advances in mechanisms research of component changes,molecular migration and protein aggregation on hardness during storage of high-protein nutrition bars. The effects of adding protein hydrolysate,protein modification,inhibiting disulfide bond,reducing molecular migration and inhibiting Maillard reaction to improve hardness changes are also summarized. In conclusion,this paper provides theoretical basis and research ideas for the future development of new high-protein nutrition bars and extension of storage period.