The Third Plenary Session of the 20th Communist Party of China Central Committee has stressed perfecting and improving the strategic mechanism for coordinated development among regions, and improving the system and policies for promoting the development of the western region to form a new pattern. At present, the imbalance and inadequacy of the development of the western region are still prominent. How to enhance regional synergy, strengthen regional economic ties and lead high-quality regional development has become an urgent practical problem to be solved in the western development. In this context, based on the concept of coordinated development, taking the synchronization of business cycle as the starting point, the degree of coordinated development in the western region is quantitatively assessed using inter-provincial mixed-frequency data from 2006 to 2020 in the western region, and based on this, the influencing factors are empirically demonstrated to provide an in-depth analysis of the coordinated development status within the region. Results of the study show that the synergistic development index of the western region shows a slow decline and sharp increase from 2006 to 2009, after which the fluctuation of the index slows down significantly, showing a slow rise and slow fall. The level of synergistic development of the northwestern and southwestern regions is obviously differentiated, and the degree of synergistic development in the northwestern region is slightly higher than that in the southwestern region. At the same time, the level of synergistic development between Sichuan and Chongqing, as an important growth pole, and Guizhou and Tibet is relatively low, indicating that its radiation capacity for less developed regions is limited. Regression estimation results show that the degree of government intervention, the similarity of industrial structure and the degree of opening up all have an impact on regional coordinated development, with the degree of government intervention and the similarity of industrial structure being the core influencing factors, indicating that the more similar the degree of local government intervention in economic development and the greater the difference in industrial structure, the more it can promote regional coordinated development. Accordingly, the following research suggestions are put forward: First, we should promote regional circulation and cope with external shocks. The second is to establish the concept of coordinated development and break down administrative barriers. The third is to implement differentiated industrial structure and eliminate homogeneous competition. Fourth, we should optimize the layout of transportation facilities and guard against siphon effect. Innovation of this paper is: From the research perspective, this paper constructs the economic cycle synergy index, which provides a new perspective for explaining the trend of regional coordinated development and examines the dynamic change process of coordinated development in the western region. In terms of research methods, the Markov-switching mixed-frequency dynamic factor model used in the article breaks through the limitation that the traditional econometrical model must adopt the same frequency data, not only uses monthly data to depict the economic operation situation in time, but also takes into account GDP, an important quarterly data indicator in business cycle monitoring, to better reflect the overall dynamic evolution characteristics of regional coordinated development. In terms of research content, on the basis of measuring the level of coordinated development in the western region, this paper discusses the factors affecting the synchronization of business cycle in the western region, which is used to judge the core factors affecting the coordinated development in the western region, so as to provide some empirical evidence and important policy suggestions for promoting regional coordinated development and preventing the further expansion of internal development gap.