Abstract: To clarify the effect of Kefir grains on the quality of the milk system in the fermentation process. Kefir particles were used as a starter in the milk system to study the effects of inoculum size,fermentation time and fermentation temperature on bovine lactate,main flavor components and rheological properties. The results showed that the effects of inoculum size,fermentation temperature and fermentation time on the fermentation of Kefir pellets were complex. Analysing the law of acidity changes shows that,under the same condition,the acidity rose with the inoculation amount increased. Electronic nose was used to measure the change of main flavor substances in fermented milk. It was found that,the lactic acid bacteria and yeast in the Kefir grains grew quickly with the temperature rising. But it would lead to deterioration of flavor. Rheometer was used to measure the viscosity and the changes of flow constant of termented milk which showed that during the fermentation process,the viscosity of Kefir fermented milk decreased with the angular frequency increasing. As temperature rising,both storage modulus G' and loss modulus G″ increased. The value of G' was greater than the other and tanδ was less than 1.The system had good elastic characteristic and coagulation. Considering the above results and economic benefits,Kefir with 0.40% inoculation volume reached the acidity of 86 °T under 30℃ for 48 h and had a good sensory quality. The final product was stable. It would have a certain guiding significance for the industrialized production of Kefir fermented milk.