Cushion plants are one kind of unique specie in alpine ecosystems. They have a compact perennial cushion structure and play a role in facilitating the survival of other associated species by improving the local micro-environment. They are called “engineers” in the alpine ecosystem and their enhancement of soil nutrient availability is one of the ways of their engineering effect. In this study, Androsace tapete, a species of cushion plant widely distributed on the Qinghai-Tibet Plateau, was selected to investigate the dynamics of this process during the growing season at elevations of 4500 m and 4800 m on the southern slope of the Nyenchenthanglha mountains in Damxung. The effects of A. tapete on soil nutrient availability were analyzed by comparing the inorganic nitrogen content, net nitrogen mineralization rate and soil enzyme activities during the growing season in the soil under A. tapete and ambient grassland (CK). The results showed three important aspects of this system. (1) Soil nitrate nitrogen and ammonium nitrogen did not show significant differences at 4500 m, but the contents of nitrate nitrogen and inorganic nitrogen under the A. tapete soil significantly increased in the middle of the growing season at 4800 m, with nitrate nitrogen increasing by 56% and inorganic nitrogen increasing by 74.5%. (2) The trend and rate of soil nitrogen mineralization were both changed under A. tapete. In the 4500 m sample site, soil net nitrogen mineralization under A. tapete was negative (nitrogen immobilization) in the middle of the growing season, and the rate was –0.11 µg g^–1 d^–1, while that of CK was positive (nitrogen mineralization) and the rate was 0.61 µg g^–1 d^–1; and the difference between them was significant. However, both were positive in the early and late growing season, and the difference did not reach a significant level. In the 4800 m sample site, the soil net nitrogen mineralization under A. tapete was positive in the early part of the growing season, and the rate was 0.07 µg g^–1 d^–1, while the mineralization for CK was negative, and the rate was –1.17 µg g^–1 d^–1; and the difference was significant. In the middle of the growing season, both of them were negative, but the soil net nitrogen mineralization rate under A. tapete (–1.95 µg g^–1 d^–1) was significantly lower than that of CK (–0.02 µg g^–1 d^–1). At the late stage of the growing season, both of them were negative, and the difference was not significant. (3) Activities of nitrate reductase and nitrite reductase in the soil were significantly increased under A. tapete. Compared to CK at the 4500 m sample site, the activities of nitrate reductase and nitrite reductase under A. tapete were increased by 9.1% and 15.7%, respectively; and they were increased by 22.5% and 16.1%, respectively, at the 4800 m sample site. The activities of these two enzymes were significantly correlated with the dynamics of inorganic nitrogen in the soil. These results indicated that, compared to CK, the cushion plant A. tapete can change the process of soil nitrogen mineralization and the content of inorganic nitrogen, but that change had seasonal dynamics and spatial differences, which implies that this process was affected not only by the engineering of the cushion plant but also by changes in the local environment. Therefore, the engineering effect of cushion plant A. tapete was not constant during the growing seasons, and further studies are needed to clarify this process, especially considering the rapidly changing climate on the Qinghai-Tibet Plateau.