The urban heat island changes in Chuxiong and Dali， two cities on the Yunnan plateau， are studied and compared with the data of air temperature， precipitation， relative humidity， average wind speed and so on from 1971 to 2000. The grey correlation degree is used to explain the causes of changes. The results indicate that the intensity of urban heat island is increasing gradually in Chuxiong in recent thirty years， while the increase in the Dali is less obvious; the monthly changes of urban heat island intensity in the two cities are basically the same: strong in dry season，weak in rainy season； the heat island intensity is strong in the daytime and weak at night in Chuxiong，but strong in the early morning and weak in the early evening in Dali.