Development and utilization of solar energy play a vital role in reducing the fossil energy consumption and greenhouse gas emissions for human being. Solar energy, which is considered as one of the most significant renewable energy resources in the future, plays a vital role in mitigating global warming. Therefore, it is extremely necessary to figure out the spatial and temporal distribution of solar energy resources in certain regions, as well as its stability so as to better develop and utilize such renewable resources. Based on daily data of solar sunshine and solar total radiation from 27 metrological stations from 1958 to 2008 and 163 radiation stations from 1961 to 2008 such as Xi’ning, Lanzhou, Xi’an, etc., our study analyzes the characteristics of the spatial and temporal variations of solar energy resources of Northwest China for the past about 50 years through completely regularized spline methods. The results indicate that the characteristics of the inter-annual and seasonal changes of solar energy resources are almost the same. According to the sunshine hours and solar total radiation, central Qinghai Province is regarded as the most abundant solar energy region, while the regions, such as southern and southwestern Shaanxi Province, belong to the unavailable region of this kind of resources. Over the past 50 years, the annual total radiation of Northwest China has decreased clearly, and the annual sunshine hours have dropped off slowly. Among 163 metrological stations, the days which the daily sunshine hours were greater than 6 hours of a month during the past 10 years added up to 45-327, of which 15 sites are more than 300 days. Solar energy resources of the southern Shaanxi Province and Urumqi are most unstable, where the K value (the index of stability of solar energy resources) is 12.21, while the border area, including the northern Qinghai Province, and the interactive zone of Qinghai, Gansu and Xinjiang, belongs to the most stable area, where the K value is 1.27. Our study suggests that the stability of the solar energy resources is consistent well with the distribution size of resource potential, that the most stable area always has the largest amount of total radiation and the longest sunshine duration.