Based on the background of “promoting harmonized development of industrialization, IT application, urbanization and agricultural modernization ”, this paper proposed the connotation of the four modernizations and their historical linkage firstly, and then analyzed the realistic choice and action mechanism of harmonized development of four modernizations in China. It demonstrated that promoting harmonized development of the four modernizations is the deepening of socialism with Chinese characteristics and the application of theory of productive forces and productive relations in new period. The integration between IT application and industrialization can impulse the development of new industrialization; the fusion of urbanization and agricultural modernization can boost the development of urban-rural integration; and promoting harmonized development of the four modernizations can advance the modernization drive on the whole. After that, this paper put forward series policies for harmonized development of the four modernizations. It presented that, governments should coordinate urban and rural development and promote harmonious relations well, crack the unfair factors of urban-rural elements exchange in future, and then the country will realize the urban-rural integration finally.