In order to screen Lactobacillus to ferment yak milk rapidly with characteristic flavor, the growth of 8 strains of wild Lactobacillus and acid production were studied. The volatile flavor composition of single-strain fermented skim milk was analyzed by gas chromatography-mass spectrometry (GC-MS). The 4 wild Lactobacillus strains could not only ferment skim milk rapidly but also provide characteristic volatile flavor to fermented yak milk, combined with the sensory analysis to evaluate the volatile flavor characteristics of the yak yogurt. The results showed that yak yogurt with high flavor preference contained higher esters and aldehydes, with esters content of 9.82μg/kg and aldehydes content of 174.64μg/kg. Acids, sulfur compounds and alcohols were lower in these samples than the others, and the contents of acids were between 366.51 and 495.84μg/kg. Meanwhile, the content of sulfur compounds was below 5.05μg/kg and the contents of alcohols were less than 1.42μg/kg. The gelation of whole yak milk took a long time in the fermentation process and the hydrolysis by lipase generated the off-flavor components, most of which are short-chain fatty acids and some ketones, etc. The strains which can result in higher levels of fruity substances such as esters, aldehydes will help to improve the quality of yak yogurt and have potential application for the development of yak dairy products.