The effect of heat island on temperature was analyzed, utilizing the temperature data of Yanan city station and Yanchang county station from 1969 to 2008. It is found that the effect of Yanan urban development on the annual average temperature can be divided into three stages: the temperature has not been affected before 1992, and its only a few from 1993 to 2002, the annual average temperature of the heat island effect contributed to 381%, after 2003 the heat island effect is obvious, more than 1 ℃, close to major cities. Heat island effects of warming temperatures in the four seasons are basically the same, heat island warming and the contribution rate are equal to the natural warming. The effect of urban heat island on the minimum temperature starts earlier, and effects are great, but it has no effect on the annual average maximum temperature. Affected by the heat island effect, not only the city temperature but also the city warming rate made the city increase the rate of warming temperatures.