With the help of statistical analysis, the changing trends between climate data from 1961 to 2006 and bud opening of Populus simonii carr.(1981-2006) were analyzed in the Inner Mongolia. Moreover, the relationships among bud opening and air temperature, precipitation and solar radiation as well as the comprehensive effects of climate factors were discussed. The results showed that there are significant regional differences．The difference of bud opening between the earliest (Luanjingtan) and the latest (Ewenki) region could be 39 days. There is a similar changing pattern in different regions with prolonged trend except Ergun, which shows an advanced trend. There is a significant negative relationship between bud opening and spring temperature. However, there are no obvious relationships between the opening and precipitation and sunlight. The air temperature and precipitation are interactive factors influencing the bud opening in the Inner Mongolia with abundant sunshine duration.