Abstract: Background The mid-altitude region of southwest Zhejiang, situated within the monsoon climate zone of southeastern China, demonstrates heightened sensitivity of carbon-water fluxes and water use efficiency (WUE) to climatic fluctuations. This ecological responsiveness stems from the synergistic interplay between altitudinal thermal gradients and seasonal precipitation heterogeneity, establishing the area as a critical observatory for deciphering ecosystem-environment interactions under dynamic climatic regimes. Methods Using eddy covariance technology, we conducted continuous monitoring of carbon-water fluxes in a representative coniferous-broadleaf mixed forest ecosystem from August 2023 to July 2024. Data analyses focused on identifying seasonal patterns and quantifying environmental controls on flux variations. Results Key observations revealed: (1) A pronounced carbon sequestration regime with annual net ecosystem productivity reaching 705.0 gCO2/m2, where gross primary productivity (GPP) exhibited temperature-mediated and radiation-dependent patterns, yet experienced precipitation constraints during peak growing seasons; (2) Hydrological cycling intensity reflected by 1148.4 mm annual evapotranspiration (ET), governed through soil thermal dynamics and atmospheric vapor pressure deficit (VPD), with precipitation acting as a periodic hydrologic amplifier during vegetative periods; (3) Emergent WUE characteristics (2.70 gCO2/mm H2O) manifesting significant intra-annual variability coupled with inter-seasonal stability, arising from the dynamic interplay between GPP's sensitivity to transient meteorological perturbations and ET's responsiveness to sustained seasonal transitions, further modulated by radiation attenuation and edaphic moisture conditions during critical phenological stages. Conclusion The studied mid-altitude mixed forest exhibits high climate resilience through optimized WUE, attributable to its heterogeneous stand structure and complementary resource use strategies between coniferous and broadleaf species. We propose two management priorities:Structural optimization: Develop multi-layered, uneven-aged mixed stands to mitigate extreme precipitation and temperature impacts on GPP through self-regulating canopy dynamics.Process-based monitoring: Implement eddy covariance networks coupled with hydrological sensors to enable real-time adjustments in silvicultural practices.