Abstract: In order to fully consider the influence of urban heat island effect on mean temperature series, the stations which located on the middle reaches of Huaihe River were selected. Huoqiu national meteological observing station and Shouxian national reference climatological stations (reference station ) were choosed as a case study.Based on the average temperature data from 1965 to 2010, the effects of urban heat island on average temperature series of Huoqiu station were analyzed by using linear regression, the cumulative distance equal method. The results showed that the average temperature series of Huoqiu station was obviously affected by urbanization of county-level city since 1994. During 1995-2010, the intensity of urban heat island was 0.30℃-0.97℃. The trend of heat island intensity increased with the lapse of time. The intensity of heat island also presented seasonal variation: the maximum value occurred in spring, followed by autumn, and the minimum occurred in winter and summer. This study suggested that the effects of urban heat island on temperature series should not be ignored in county-level city of the middle reaches of Huaihe River.