Using the data of monthly sunshine duration from 1953 to 2005 in Lhasa of Tibet, the interannual and interdecadal variations of the annual and seasonal sunshine duration are analyzed by means of the linear trend analysis method. The results show that the decreasing trends of the annual and seasonal sunshine duration were different during recent 50 years. The annual decreasing rate was 27.6 h/10a, and the trend is still getting stronger, especially in summer and autumn. The anomalies of annual sunshine duration were positive from the 1950s to 1980s, and became negative in the 1990s. The sunshine duration was obviously less in summer of the 1990s, abundant in winter of the 1960s. The annual sunshine duration was less than normal at the end of the 1990s, extremely less in 1998 and 2000; while there were more anomalous years in winter mainly in the 1950s. The results show that there was a decreasing trend in total annual mean cloudiness and low cloudiness.