Abstract: Too much negative information leads to a huge gap between food safety risk perception and the real situation. Based on the information supply and demand theory, this paper gives an explanation for this phenomenon by bringing food safety information characters into media and consumers' decision function. The result shows that the bias is caused by rational ignorance and excess demand for negative information. Limited by individual information processing capabilities, costs of information access and the inconsistence between personal position and media ideology position, consumers' information demand for food safety presents the character of rational ignorance initiatively. The analysis based on the law of diminishing marginal utility and risk aversion shows that consumers' demand for food safety negative information is greater than that for positive information. The empirical analysis on traditional print media shows that due to the different ideology positioning, food safety information supplied by various types of media are quite different and that social media has amplified the presence of food safety negative information.