Based on CO₂ fluxes measured with the eddy covariance technique, we analyzed the relationship between gross primary productivity (GPP) and growing season degree days (GDD) at different time scales over an alpine wetland in the Qinghai-Tibetan Plateau during the growing season from 2004 to 2016. The daily and monthly GPP and GDD in the growing season showed a single peak trend over the alpine wetland ecosystem. The maximum daily and monthly GPP and GDD values all occurred in July or August, while the minimum value occurred in May. However, GPP and GDD showed no obvious trends during the growing season. The mean values of seasonal GPP and GDD for the entire growing season from 2004 to 2016 were (458.82±25.78) gC m^-2 season^-1 and (1060.89±84.07) ℃.On the daily, monthly, and growing season scales, all GPP values positively correlated with GDD (P < 0.01). However, on comparing GPP and GDD in each month of the growing season, no significant correlation was found between GPP and GDD in May and September (P > 0.05), while the correlation was strongest (P < 0.01) in July. Overall, the GPP of the alpine wetland ecosystem indicated a positive reaction to the thermal condition, suggesting that the photosynthetic capacity of the wetland ecosystem in the Qinghai-Tibet Plateau could improve in the future under the effect of global warming.