Investment in agriculture, forestry, animal husbandry and fishery, mechanization level, fertilizer, plastic sheeting, and agricultural science and technology in agricultural production are important input elements. These elements are put into the extended C-D production function model. It gets the function of agricultural production in China by ridge regression calculation based on agricultural production data from 2000 to 2019. It confirms that the function of agricultural production is robust with variable substitution and adjustment research period. In the process of agricultural modernization in China, the output elasticity of the investment in agriculture, forestry, animal husbandry and fishery, application amount of fertilizer, usage of plastic film, total mechanical power, and agricultural science and technology level to total agricultural output value were reduced. The coefficients were 0.383, 0.269, 0.213, 0.161, and 0.051, respectively. The agricultural output contributions of agricultural science and technology level, investment on agriculture, forestry, animal husbandry and fishery, usage of plastic film, total mechanical power, and application amount of fertilizer on total agricultural output value are 21.392%, 20.681%, 15.444%, 13.295%, and 8.684%, respectively. Therefore, it is necessary to increase investment in agricultural science and technology, increase investment in agriculture, forestry, animal husbandry and fisheries, and increase subsidies for the use of new machinery and power in order to promote the process of agricultural modernization.