With the development of urbanization, Xining, the largest city on the Qinghai-Tibet Plateau, its urban heat island effect and impact are increasingly obvious in recent years. Based on hourly temperature data from meteorological observation stations in Xining city and suburbs, this paper analyzed the variation characteristics of daily and hourly average heat island intensity of average temperature, maximum temperature and minimum temperature in Xining city. The results show:(1) Compared with the suburbs, the average temperature in Xining city had a small change within a day, showing a weak cold island effect from 16:00 to 17:00. The intensity of cold island was 0.034℃, and the intensity of heat island was strongest from 06:00 to 07:00 before sunrise, with the highest intensity of heat island reaching 3.01℃; (2) Both spring and summer were heat island effects in one day, and the change range of heat island effect in one day is small, 2.76℃ and 2.12℃, respectively. The intensity of heat island was strongest in autumn and winter at 07:00-08:00 before sunrise, which are 2.89℃ and 4.14℃, respectively. The cold island effect was shown in autumn at 16:00-17:00 and winter at 15:00-17:00, and the maximum cold island intensity is 0.34℃ and 0.53℃, respectively. (3) The strongest mean temperature UHI intensity was 3.40℃ at the third five-day in January, and the weakest UHI intensity was 1.07℃ at the second five-day in July. The UHI intensity showing obvious at the third five-day in January was 0.88℃, and it showing weakest at the first five-day in September was 0.13℃ in the day. But in the night, the maximum UHI intensity was 5.92℃ at the third five-day in January, and the minimum value was 1.62℃ at the second five-day in July. So the variations range of seasonal UHI intensity in the night was obvious than in the day, and the value was 4.30℃ and 0.75℃; (4) The average extreme maximum temperature showed UHI effect in spring and summer, and the average UHI intensity was 0.58℃, but it showed urbane cold island effect in autumn and winter, and the value was 1.84℃. The average extreme minimum temperature showed UHI effect all the time, and the UHI intensity was 3.22℃and 5.11℃ in summer and winter.