Abstract: Using the probiotic yogurt added with Lactobacillus casei in place of the traditional yogurt only including Lactobacillus bulgaricus and Streptococcus thermophilus, and determine the optimum process conditions of main factors such as strains inoculating proportion, inoculation amount, fermentation temperature and fermentation time by using single factor and orthogonal experiment. According to the changes of the pH and the acidity in the fermentation process and after ripening, and take the texture, the sensory score and the viable count of the probiotic yogurt into consideration, determined the optimum process conditions by the range analysis and variance analysis. The optimum process conditions were as follows:lactobacillus (Streptococcus thermophilus∶Lactobacillus bulgaricus=1∶1) ∶Lactobacillus casei=2∶1, inoculation amount 3%, fermentation temperature 40℃, fermentation time 9h. In the optimum process conditions the sensory score of yogurt reached 93.65 points, and firmness, consistency, cohesiveness and viscosity were 138.975g, 3448.022g·s, 99.018g and 299.117g·s respectively, the acidity and viable count also reached 122°T and 3.13×1011cfu/mL after ripening 24h. It was showed that the optimum technological parameters were reliable, and it had practical significance.