Abstract: With Gansu Tianzhu yak milk as a raw material and the 70% lactose hydrolytic percentage as experiment index, the hydrolysis condition of yak milk was optimized by changing the dosage of enzyme and hydrolysis time at different temperatures.In addition, with the 5- Hydroxymethyl Furfural ( 5- HMF) as indicator of Maillard reaction, adding different types of inhibitors, the indicatory effects of inhibitors was evaluated by measuring the inhibition rate of 5- HMF.The results showed that on the condition of 40℃, 0.15% enzyme concentration and 3h hydrolysis time, the lactose hydrolytic percentage reached 71.1%. Moreover, under the condition of 6℃, 0.20% enzyme concentration and 20h hydrolysis time, the lactose hydrolytic percentage reached 71.3%.Under the heat treatment condition at 85℃ for 10min, vitamin E, BHT, methionine and cysteine all had inhibitory effects on the Maillard reaction in low lactose yak milk but the ascorbic acid could promote the Maillard reaction, and the inhibitory effect of methionine and cysteine were significant.