AbstractGlobal warming is dramatically altering the plant phenology of terrestrial ecosystem and thus has caused significant effects on the terrestrial carbon cycle. Many studies have investigated the relationships between the spring phenological changes and the dynamics of carbon cycle, but the seasonal differences in these relationships are still unclear. This study used eddy covariance measurements of grassland net ecosystem productivity (NEP) from nineFLUXNETsites (73 site‐years of data) to investigate the relationships between the spring phenological changes (i.e., early green‐up,EGU; middle green‐up,MGU; and late green‐up,LGU) and the dynamics of carbon cycle (includingNEP; ecosystem respiration,ER; and gross ecosystem production,GEP) at a ten‐day scale. Weak relationships were found between the spring phenological changes and the dynamics ofERat all sites. The advance of spring phenology mainly caused significant increases inGEP(orNEP) during the initial 20–50 d after the green‐up date at most sites. With an advancement of 1 d inEGU(MGUandLGU),GEPandNEPwere increased by 1.5–6.0 (3.5–7.1 and 2.4–4.7) and 0.7–3.6 (1.5–3.9 and 1.9–4.7) g C/m2during the early growing season (EGS), respectively. The advance of spring phenology did not have significant impacts onGEP(orNEP) during the middle and late growing season (MGSandLGS) at most sites, but yielded a significant decrease inGEP(orNEP) duringMGSat a few sites. As the grasslands turning green, the duration of the impact of the changes inEGU,MGU, andLGUonGEP(orNEP) was reduced, whereas the magnitude of the impact of the changes on the ten‐day cumulativeGEP(orNEP) was increased at most sites. Thus, there were two possible impact models for the spring phenological changes on the dynamics of carbon cycle for grasslands: The advance of spring phenology only increases theGEP(orNEP) duringEGS, and the advance of spring phenology only decreases theGEP(orNEP) duringMGS. These results could be helpful in further understanding the influences of spring phenological changes on the dynamics of carbon cycle for grasslands.