Abstract: The quantitative approach,characteristic of precision,is used in many areas in modern social science,and it has also penetrated into our daily life and work,such as in media survey or college teaching quality review.But by comparing study of two investigating cases,this paper argues that the quantitative approach in social science,especially the investigations involving social evaluation,cannot guarantee the veracity of the results calculated by complex formulas,with the objects studied abstract,the medium language vague in nature,and the measurements diverse;while in natural science,the objects studied are constant and usually concrete,the measurements are unified and precise and can be conversed mutually.