The nonparametric MannKendall trend test is applied to examine the trend of diurnal temperature range (DTR) of Dalian from 1961 to 2005．The method of correlative analysis is used to analyze the factors influencing DTR. The results show: (1) The trends of mean DTRs in four seasons showed a statistically significant decrease, especially in autumn and winter, the least significant in summer. But the mean, maximum, and minimum temperatures in four seasons had a statistically significant increasing trend in four seasons, and the trends of minimum temperature were much larger than those of maximum temperature. (2) DTR was negatively correlated with wind speed closely, as well as with minimum temperature, cloud cover, and vapor, but correlated with maximum temperature positively. (3)The factors related to the trends of DTR vary with season. In spring and summer, the trend of DTR is more closely correlated with the trend of maximum temperature than with minimum temperature, but in autumn and winter, the increasing trends of minimum temperature are more significant than those of maximum temperature. In spring, the increasing trends of wind speed and water vapor pressure contribute to the increasing trends of DTR, and in summer and autumn, the increasing trend of cloud cover is another cause of DTR decrease.