The formation of alpine timberline has always been in focus in alpine mountain forest ecology, and the threshold temperature of tree growth at timberline has always been a hot spot of research. We used the radial growth data of Minjiang fir (Abies faxoniana) at the timberline of Gonggang Mountain, Jiuzhaigou, Western Sichuan Plateau to test the effects of threshold and accumulated temperatures on Minjiang fir growth through the response function analysis. The results showed that the radial growth of Minjiang fir is mainly limited by temperature. Furthermore, the radial growth positively correlated with temperatures during the growing season (July-September), during winter (previous December-February), and in September and October of the previous year (P < 0.05). However, the effect of precipitation on Minjiang fir growth was weak. The fir radial growth negatively and positively correlated with the first and last days of growth at different threshold temperatures, respectively. The strongest correlations between fir growth and the first and last days of growth at different threshold temperatures occurred at 9.5 and 6.5℃, respectively. The fir radial growth at timberline also positively correlated with the accumulated temperatures (starting at 7, 7.5, 8, 8.5, 9, and 9.5℃) and the duration at 9.5℃ (P < 0.05), which indicates that 7-9.5℃ might be the threshold temperature of cambium activity, especially the temperature of 7℃ might be the initial temperature of photosynthesis and growth of Minjiang fir at the timberline. The growth period of Minjiang fir at timberline is from the mid-April to the beginning of October. With a significant increase in temperature after 1980, the accumulated temperature during the growing season began to increase, the first day of growth has shifted to an earlier date (4.6 d/10a, r²=0.19, P=0.01), the last day of growth has been postponed (1.8 d/10 a, r²=0.04, P=0.25), the growing season has become longer (6.4 d/10 a, r²=0.19, P=0.01), thus, significantly promoting the radial growth of Minjiang fir at the timberline. The results suggest that future climate warming might increase tree growth at the timberline in the West Sichuan Plateau, and the timberline might move upward.