The 20th Central Committee of the Communist Party of China (CPC) adopted the"Resolution of the Central Committee of the Communist Party of China on Further Deepening Reform Comprehensively to Advance Chinese Modernization" at its third plenary session,and stressed to establish sound systems and mechanisms to foster new quality productive forces in line with local conditions. As an important plan and key point for China’s economic development to achieve high-quality development under the new situation, the development of new quality productive forces must not lead to the situation of a headlong rush into projects, similar industrial structures and cut-throat competition. On the contrary, it is necessary to explore comparative advantages and appropriate paths by combining various factors such as natural resource endowment, geographical ecological environment, population education level, digital infrastructure, and innovation and R&D capabilities. As an important constraint on national security and long-term development, the development of the western region is relatively lagging behind in the process of Chinese modernization, which affects the overall level of high-quality development of China’s economy. The nine western urban agglomerations are the important power source of the development of the western region of China, and also the highland for the western region to seize the development opportunity of new quality productive forces. Based on the panel data of cities in western China from 2012 to 2022, this paper constructs a comprehensive evaluation system from the three dimensions of scientific and technological productivity, green productivity and digital productivity, and the entropy method is used to measure the development level of new quality productive forces and the index scores of each dimension in the nine urban agglomerations in western China. The Dagum Gini coefficient method, kernel density estimation method, Markov transition probability matrix, σ convergence model and β convergence model are used to investigate the spatial-temporal characteristics, source of differences, evolution rules and convergence mechanisms of the development level of new quality productive forces in urban agglomerations in western China. The study finds that, on the whole, the development level of new quality productive forces in urban agglomerations in the western region shows an increasing trend year by year, but the overall level is low and shows obvious gradient difference. And there is a structural decomposition feature that the level of scientific and technological productivity is the highest, the level of digital productivity is the second, and the level of green productivity is the last. In terms of relative differences, the overall differences in the development level of new quality productive forces in western urban agglomerations are relatively significant, among which the hypervariable density and inter-regional differences are the main sources of regional differences in urban agglomerations. In terms of absolute difference, the spatial difference of the development level of new quality productive forces in western urban agglomeration has a trend of further expansion, and there is a phenomenon of "club convergence" and a certain degree of "Matthew effect". In terms of convergence characteristics, in the short term, the gap of the new quality productive forces level in the western region has not narrowed, but in the long term, there are absolute and conditional β convergence trends, that is, the new quality productive forces level in the western urban agglomeration will converge to the steady state level in the long term. Therefore, in the process of cultivating and developing new quality productive forces, the western region should not only tap its characteristics and advantages according to local conditions, but also promote coordinated development through overall planning and cooperation.