The lapse rate of near surface air temperature is an important parameter in hydrologic and climatic simulations, especially in the high mountainous areas without enough observations. Based on the long-term meteorological measurement data (1951-2013) and near surface air temperature (T_(min), T_(ave), and T_(max)) measured by self-established weather stations during 2012-2016, this study evaluates the spatial and temporal variations of near surface temperature lapse rate (betalocal) over the northwestern Tibetan Plateau. The results show that: 1) The near surface air temperature lapse rate has a spatiotemporal distribution pattern over the northwestern Tibetan Plateau and the constant environmental temperature lapse rate (0.65 ℃/ 100 m) throughout the year cannot represent the variability of the temperature-elevation relationship in complex terrain areas. The temperature has a significant downward trend as the elevation increases. LRT_(ave), LRT_(min), LRT_(max) in two regions showed different spatial variations. The LRT_(ave), LRT_(min), LRT_(max) at the meteorological stations are higher than the LRT_(ave), LRT_(min), LRT_(max) at the mountain observation stations. The LRT_(min) shows significant spatial variation, while the LRT_(max) has smaller spatial variation. 2) A significant seasonal variation can be observed in this region. At the meteorological stations, the trend is that higher values are observed in spring and summer and lower values in winter. As for the mountain observation stations, the LRT_(ave), LRT_(min), LRT_(max) are higher in summer and lower in winter. The LRT_(max) at the meteorological stations and the LRT_(min) at the mountain observation stations have significant seasonal variations. 3) The variations of betalocal for T_(max) and T_(min) in two regions exhibit similar monthly variation characteristics, that betalocal is lower in months of winter and spring and higher in other months. Monthly betalocal for T_(min) is higher than T_(ave) and T_(min) at the meteorological stations through the whole year. The highest betalocal for T_(max) and T_(min) occurs in April, while the highest betalocal for T_(ave) occurs in June. At the mountain observation stations, the highest betalocal for T_(max) occurs in October, while the highest betalocal for T_(ave) and T_(min) occurs in April. 4) A significant increasing trend of betalocal for T_(ave) and T_(min) was observed after 1990. The difference of betalocal for T_(min) before and after 1990 is more obvious. The differences of T_(max) at different elevations before and after 1990 are weak. 5) The spatial and temporal variations of betalocal over the northwestern Tibetan Plateau are linked to geographic differences and climate factors. In addition, the controlling factors for the lapse rate in two regions are different. This research will provide a theoretical basis for quantitative researches of temperature distribution characteristics and mountain ecosystem's response to climate change in mountain areas.