Changes in seasonal freeze?thaw pattern under climate change scenarios might lead to nitrogen loss via leaching in cold biomes, and in turn alter the cycles of soil nutrients and water environment of forest streams. In order to understand the effects of seasonal freeze?thaw cycles and their changes in seasonal freeze?thaw pattern on the soil nitrogen loss from leaching in the alpine forest, soil columns were sampled from an alpine forest with 3600m altitude. The soil columns were then incubated in the forest floor at the sites of 3600 m (A1), 3300 m (A2) and 3000 m (A3) altitudes to simulate climate warming induced by elevation decreasing. Soil nitrogen loss from leaching in three sites was measured at four critical periods as temperature changed in the freeze?thaw season and the growing season from May 2010 to April 2012. The results indicated that the loss of soil nitrogen via leaching increased with the increase of altitudes, and showed the order as: (1. 85 0. 39) kg·hm~(-2)·a~(-1) (A3) < (1. 87 0. 34) kg·hm~(-2)·a~(-1) (A2) < (2. 94 0. 73) kg·hm~(-2)·a~(-1)(A1) in the alpine forest of Western Sichuan. More than 62% of annual nitrogen loss from leaching was observed in the freeze?thaw season. Moreover, the lost nitrogen in the freeze?thaw season was mainly in the form of ammonium and nitrate, and more ammonia lost from leaching was detected compared with nitrate. In contrast, soluble organic nitrogen was the main component in the lost nitrogen in the growing season. The results demonstrated that seasonal freeze?thaw cycles greatly controlled the soil nitrogen loss from leaching in the alpine forest. The results here also imply that nitrogen content will decrease in forest soil, but increase in the forest stream in this cold alpine forest in the scenarios of climate warming.