BVN is a computational error in the processing of percentages. The influencing factors of BVN can be divided into three types: individual factors, stimulus factors and condition factors. In the research of individual factors, previous literature focused on the influence of individual mathematical ability but neglected the influence of knowledge base, such as mastery of the mathematical principle of promotion. About stimulus factors, researchers focused on the influence of difficulty of calculating caused by percentages changing, but neglected the difficulty of price expression. Base on the above review, this study examined the influence of knowledge base and difficulty of calculating which was manipulated by price. 150 undergraduate students participated in this study. The study used a 2 ×3 mixed design, in which the difficulty of calculating (low and high) was a within-subjects variable and knowledge base (BVN phenomenon, mathematical principle, control) was a between-subjects variable. We used the prices of products to manipulate the difficulty of calculating, the price which was 3.89 yuan/50g was set as the price of high difficulty and the price which was 5 yuan/50g was set as the price of low difficulty. In this experiment, participants were randomly assigned to three groups. All groups read the materials firstly. Material of BVN group was introducing the phenomenon of base value neglect; material of math group demonstrated how to calculate preferential benefits of the bonus back and the price discount; material of control group was irrelevant with BVN or promotion. After reading the materials, participants finished the questionnaires. The questionnaires had two situations, and in each situation, there were two brands of the same product but adopting different promotion ways. In one situation, the price of product was 5yuan/50g, whereas in the other situation, the price of product was 3.89yuan/50g. In each situation, participants were asked to rate their evaluation of the two types of the economically equivalent promotion (50% bonus back and 33% price discount) on -5 (the bonus back has more preferential benefits) to 0 (the preferential benefits of the bonus back are same to the preferential benefits of the price discount) to 5 (the price discount has more preferential benefits) scales. If the score of the participants’ evaluation is significantly less than 0, the participants neglect the base values and have the BVN mistakes. After finishing the questionnaires, participants were asked to rate the difficulty of calculating preferential benefits of the two types of promotion under the two prices of products on a 1(very easy) to 7 (very difficult) scale, so as to check the manipulation of calculation difficulty. It was showed that: (1) when consumers only learned about the phenomenon of BVN, the errors appeared regardless of high or low difficulty of calculating; (2) when consumers only learned about the mathematical principle of promotion, the errors appeared only in the condition of high difficulty, but in the condition of low difficulty, the errors was not found; (3) learning about the mathematical principle of promotion could reduce the tendency of base value neglect.