In order to study the relationship between water distribution change and water retention properties of yak meat during postmortem aging, explore the mechanism of water holding capacity (WHC) after slaughter, 10 male yak in Qinghai Province were slaughtered and aging within 4℃, then the pressing loss, drip loss, cooking loss and surface hydrophobicity index were determined during different aging times, and the water distribution was analyzed by lowfield nuclear magnetic resonance (LF-NMR) and nuclear magnetic resonance imaging (MRI), beef cattle were control group. The results showed that the pressing loss, drip loss, cooking loss and surface hydrophobicity index got the maximum value on the third day, which was significantly higher than other time points （p<0.05). It had the worst water holding capacity. Water distribution showed that at the early stage of postmortem aging, P22 was decreased and P23 was increased, at the later stage of postmortem aging, P22 was increased and P23 was decreased, in addition, P22 and P23 had a significant negative correlation （p<0.05), it indicated that the phase transitions existed between two kinds of moisture during postmortem aging. Nuclear magnetic resonance imaging reflected the spatial distribution of water, and the optimal maturity time was determined as 5 d, at this time, the image gray value was the highest and WHC was the best. Through comparative analysis, it was found that the WHC of the beef cattle was better than that of yak meat during the whole aging.