Infant formula provides the necessary nutrition to the baby. It is very important for parents to choose the right milk powder. There are kinds of ways to buy the infant formula, but buying on line is the most convenience way. Studying the influence factors for online buying milk powder can guild the parents' purchase intense, provide the reference information to the vendor and also can build a healthful environment. In this study, Literature Analysis Method, Depth interviews, questionnaire survey was used. 336 parents were surveyed by questionnaire, including 117 males, 219 females. In this study, the procedures SPSS13.0 version was used for descriptive statistics, t test and multiple hierarchical regression analysis. The main findings of this study as follows: 1. The top three factors of influence factors are quality of the milk powder, the brand of the milk powder and the nutrition of the milk powder; 2. Education level, internet age are high related to choose imported milk source, other population statistics index were not significant; 3. Gender is significant to Familiarity, Trust, Trust tendency, satisfaction, purchase intention. That is to say female is more familiar with the online web, more trust to the web and have high trust tendency, more satisfaction and purchase intention; 4. Familiarity, trust, trust tendency, satisfaction and purchase intention correlated significantly between them; 5. Trust is mediator between trust tendency and purchase intention; 6. Familiarity, trust and satisfaction is significant effect on purchase intention, but trust tendency is not significant to purchase intention.