Abstract: Based on the single factor experiment,the process and formula of purple potato yogurt were optimized by response surface experiment design using fuzzy mathematics sensory score as response. The results showed that the best process and formula were:Lactic acid bacterium added 0.46%,6.09 h for fermentation,sucrose added 7.66%,purple potato powder added 5.90% and milk was added to make up to 100%. Analysis of variance showed the effect of factors on the sensory score of purple potato yogurt:The amount of lactic acid becteria added > the amount of strain added > the fermentation time > the amount of purple potato powder added. Through the principal component analysis of the texture index of purple potato yogurt,two main components were extracted and an evaluation model for the quality of purple potato yogurt was constructed. The results showed that it was feasible to use this model to judge the quality of purple potato yogurt.