Maintaining moderate economic growth targets (EGTs) is the key for local governments to effectively implement the “carbon peak and carbon neutrality” goals under the refreshed development pattern. Utilizing panel data of 276 prefecture-level cities in mainland China from 2010 to 2020, and employing methods such as intermediary and threshold models, this study empirically analyzes the internal mechanism of EGT’s impact on urban carbon productivity (UCP). Our findings demonstrate that: ① The overall EGT during the analyzed period is not conducive to improving UCP. This conclusion remains valid after a series of robustness tests. This effect is more pronounced in the central region and resource-based cities than in the east-west region and non-resource-based cities. ② EGT not only directly suppresses UCP but also exerts indirect negative impacts on UCP from three aspects: delaying the digital economy (DE), constraining financial expansion (FE), and hindering green technology innovation (GTI). This negative indirect effect is similar to or even surpasses the direct effect, suggesting that the internal relationship between EGT and “dual-carbon” goals should be re-evaluated from a new compound perspective. ③ EGT not only has a simple linear impact on UCP but also significantly exhibits a dynamic evolution pattern in inverted “U” shape. That is, as EGT continuously upgrades, a nonlinear impact on UCP emerges in the form of “promoting first, suppressing later”. This indicates that surpassing the “degree” limit for EGT will be detrimental to the improvement of UCP. This study broadens the scope of carbon productivity analysis by introducing a new perspective centered on EGT. The insights gleaned from this research offer valuable guidance for local governments to effectively manage economic growth expectations and promote the synchronized achievement of dual-carbon objectives.