Against the backdrop of intensifying global climate change and worsening greenhouse effects, the development of low-carbon city models has emerged as a critical breakthrough in mitigating the climate crisis. This study utilized panel data from 286 prefecture-level cities in China from 2012 to 2022, employing the super-efficiency SBM model with undesirable outputs and spatial autocorrelation models to measure eco-efficiency and characterize its spatial correlations. By integrating static and dynamic spatial Durbin models, the research delved into the spatial driving mechanisms, dynamic temporal effects, and regional heterogeneity of low-carbon policies on eco-efficiency from a dual spatiotemporal perspective, thereby addressing research gaps in quantifying spatial spillover effects and analyzing time-lagged characteristics. The findings reveal: (1) From the spatiotemporal evolution of eco-efficiency, the overall eco-efficiency of the sampled cities exhibited a fluctuating upward trend from 2012 to 2022, with a distinct "high in the east and west, low in the center" gradient pattern and strong spatial agglomeration effects. (2) The impact of low-carbon policies on ecological efficiency has the dual characteristics of "local gain-neighborhood inhibition", and there is significant regional heterogeneity. Specifically, the positive effects of low-carbon policies become increasingly significant as the economic level of cities improves. (3) The empirical results of the dynamic spatial Durbin model show that urban ecological efficiency has a significant "time lag" effect, and the long-term impact of low-carbon policies on ecological efficiency is greater than the short-term impact. In terms of regional heterogeneity, the long-term impact of low-carbon policies in the eastern region is greater than the short-term impact, while the short-term effect in the central region is more significant. (4) Mechanism analysis reveals that green technological innovation and overall industrial upgrading contribute to strengthening the promoting effect of low-carbon policies on urban ecological efficiency and have a significant threshold effect, but the promoting effect on adjacent cities is not significant. This study has promoted the paradigm shift of the impact of low-carbon policies on ecological efficiency from "presence or absence of effects" to the multi-dimensional coupling effect research of "intensity-space-time series", forming a complete research chain of "efficiency measurement-effect identification-mechanism analysis".