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Sunshine duration is one of the elements that characterize the strength of solar radiation, and it is closely related to the utilization of light and heat energy in agriculture. The temporal and spatial variation of annual and seasonal sunshine duration in Tianshan Mountain and its causes are analyzed by using the method of anomaly variation trend, 5years moving averge, MK test and IDW residual error revision by ArcGIS, based on sunshine duration, precipitation, temperature, cloudiness, wind speed and relative humidity of 55 meteorological stations from 1961 to 2015. The conclusions show: (1) Annual and all seasonal, except in spring, variations showed a declined temporal trend. The differences in the Tianshan Mountain were significant, and the trends in the mountain area and the northern slope of the Tianshan Mountain were more obvious than that in the southern Tianshan. (2) The MannKendall mutation test shows that in recent 55 years, the mutation times of annual sunshine hours in the northern slopes of Tianshan Mountains, the sourthern slopes of Tianshan Mountains and the mountain areas were 1985, 1980 and 1988. In spring, only the mountainous area was mutated. And in winter, only the southern slopes of the Tianshan Moutains and the sunshine hours in the montains were mutated. The results show that the cloud cover and precipititation were the leading factors in the occurrence of muations. (3) There was obvious regional differences in the climatic distribution of seasonal and annual sunshine duration; generally, the sunshine duration of Tianshan Mountain showed a increasing trend from west to east and those of the plains were reater than ththose of mountain areas. In spring, the sunshine duration was higher in northeast than in southwest. In summer, the spatial distribution of sunshine duration was similar with spring, high in northeast and low in southwest. In autumn, the sunshine duration increased from south to north and higher in east than in west. The distribution of sunshine duration in winter reduced from south to north gradually. (4) The factors of precipitation, cloud amount, relative humidity showed a negative correlation with sunshine duration. There were positive seasonal correlation between sunshine duration and wind speed in the Tianshan area, except in spring. In recent 55 years, the amount of clouds and precipitation changed significantly, which were the main factors leading to the decrease of sunshine duration in the Tianshan area. The number of sunshine hours changed significantly in Tianshan Mountain.