Abstract: Under the background of the aging and reduction of the agricultural labor force, agricultural mechanization is increasingly important to ensure the safety of agricultural production capacity and supply of agricultural products, to maintain balanced development among different industries, and to improve international competitiveness. Based on a provincial panel data of 28 provinces in China and applying the fixed effect model, this paper estimated the Cobb-Douglas function of crop industry, calculated, and discussed the contribution rate of agricultural mechanization to the crop industry output in each province and China. Results show that the level of mechanization decreased slightly from 1979 to 1984 due to that the original large-scale machinery was not suitable for the new small-scale production mode with the popularization of the household responsibility system. After 2004, the central government attached great importance to agriculture and increased subsidies for purchasing agricultural machinery, which accelerated the rise of mechanization and increased the total output value of the crop industry. In most provinces of China, agricultural mechanization plays an important and positive contribution to the output of the crop industry from 1979 to 2018, even there were five provinces’ contribution rates more than 30%. Both the calculation results of provincial data and national data show that the contribution rate of national agricultural mechanization to the crop industry was positive over the years, and the contribution rate of agricultural mechanization to the total output value of the crop industry was much higher than other factors, such as chemical fertilizer, land, and labor. Total national data also shows that: compared with 1979, agricultural machinery contributed as much as 54.196% of the total output value increment of the crop industry in 2018. Therefore, this paper suggests: to enhance supporting policies, to increase infrastructure construction such as well-facilitated farmland and tractor roads, to strengthen the level of agricultural mechanization in weak areas, and to improve the development quality of agricultural mechanization.