Abstract: This paper analyzes the changing characteristics of the temperature and rainfall of Mengzi according to the meteorological information obtained from the weather observatory in Pinbian County of Mengzi from 1951 to 2002.The results indicate that there is urban heat island effect in Mengzi and it is increasing year by year.Through the investigation,we know that the average intensity in Mengzi is 1.56 ℃.It is strongest in spring and weakest in summer.It is strongest at 08:00 and weakest at 14:00 in a day.This article uses gray connection analysis method to analyze the main weather factor which affects this urban heat island in Mengzi.At last,it comes to the conclusion that the velocity of wind is the main weather factor.