[Objective] Scientifically assessing the county-level comprehensive development quality is a key step in advancing new urbanization and achieving regional coordination and sustainable development. [Methods] Based on the core connotations of new urbanization and synergistic development, an evaluation framework for comprehensive development quality was constructed from a three-dimensional perspective of "society-landscape-ecology". Methods such as the theil index, exploratory spatiotemporal data analysis (ESTDA), and the barrier degree model were comprehensively applied to analyze the spatiotemporal patterns and diagnose the barrier factors of comprehensive development quality across 102 county-level units in Shanxi from 2012 to 2023. [Results] (1) The comprehensive development quality of counties in Shanxi Province showed a slow upward trend, with an average annual growth rate of 1.28%. Spatially, it exhibited a pattern of "large dispersion with small concentration", with high-level areas clustered in the central region and southeastern Shanxi, while low-level areas were distributed in the Yuncheng Basin. (2) Overall regional differences displayed a fluctuating convergence trend, but 62.75% of the differences originated from within prefecture-level cities, with intra-city disparities in Jincheng, Lüliang, and Changzhi showing an expanding trend. (3) Global spatial correlation was significant but continuously weakened, and the local spatial structure exhibited strong characteristics of "path dependence" and "spatial lock-in". (4) Social development quality is currently the most constraining dimension, with the total postal and telecommunications services, total profits of industrial enterprises above a designated size, and fixed-asset investment per unit land area identified as the three core barrier factors. Meanwhile, the constraining effects of ecosystem and landscape pattern quality are gradually becoming apparent. [Conclusions] The comprehensive development quality of counties in Shanxi Province has improved but still faces challenges such as internal imbalances, spatial lock-in, and multidimensional constraints. Future efforts need to coordinate socio-economic development with ecological protection to achieve three-dimensional synergistic enhancement.