The quantitative theory of optimum doping content of transparent conductive films was introduced. In this theory, the relationship of one of the physical properties with crystal structure, preparation method and doping content was set up. The parabola equation that can be fixed to the test curve and has reliable physical meaning was given. The extreme value of this equation just determined the quantitative relationship between the optimum doping content, crystal structure and preparation method, and the expression of the optimum doping content was obtained accordingly. The experimental results of doping modified for WO 3 electrochromic films were analyzed. Using this expression to calculate the optimum doping content in WO 3 electrochromic films, the quantitative calculation results are in accordance with the experimental results. This theory is also appropriate for the optimum doping content problems of other materials.