Abstract: Based on the single factor and orthogonal experiment, the optimal pure raw milk and fermentation conditions Lactobacillus casei KL1 fermented yogurt were determined. The optimized screening of raw milk was M2, at the same time by adding milk powder ( M6) to improve color and structure of yogurt. Using three factors and three levels of L9 ( 34) , the optimization of fermentation process of yoghurt orthogonal experiment, inoculation amount was the main factor affecting the quality of yoghurt fermentation KL1, the following optimized conditions of Lactobacillus casei KL1 fermented yogurt determined that the inoculation rate was 6.0%, the amount of M61.0%, glucose 1.5%, 37 ℃ for 22 h, the number of viable bacteria in probiotic yogurt was about 10 times as high as that of the optimized yogurt before the fermentation.