Postmortem aging is an important method for improving meat quality. In order to provide theoretical basis for improving meat quality, the experiment was conducted to determine the termination of postmortem aging for yak meat by measuring pH value, and to investigate the differential proteomics between fresh and postmortem aging yak meat. The Longissimus dorsi from Qinghai Datong yak was used to determine proteomic by ultracentrifuge and twodimensional electrophoresis. Imagine analysis for selection of differentiallyexpressed protein spots was conducted by PDQuest 8.0 software. Proteins were identified by ion trap mass spectrometry equipped with surveyor HPLC system. The results showed that fiftyfour spots from electrophoresis gels were selected as differentiallyexpressed proteins for MS analysis, and eighteen proteins were identified, in which forteen proteins showed downregulated expression, one protein only expressed in fresh meat and three proteins only expressed in postmortem aging meat. These differentiallyexpressed proteins separated in this study involved metabolic, structural, and stress related proteins. The research proved that metabolic, structural, and stress related proteins had varied abundance during postmortem aging in Longissimus dorsi of Qinghai Datong yak. In summary, the study contributes to clarify the mechanism involved in the aging process of yak meat.