Abstract: Based on R/S analysis and comparison between city and suburb, climate characteristic in Lanzhou city, Gansu Province was studied, the influences of urbanization on several climate elements in different season were calculated and the future trends of climate in Lanzhou were forecasted. The main conclusions are： (1) In the past 49 years, the long climate trend of Lanzhou city was consistent with that of Northwest China, the whole country and the Northern Hemisphere, the winter temperature and the annually mean temperature were ascending at the rate of 0.72℃/10-year and 0.28℃/10-year respectively, and the summer mean temperature was descending at a rate of 0.036℃/10-year. (2) The mean temperature, water vapour pressure, relative humidity and sunshine percentage in winter (January), summer (July) and annual mean from 1951 to 1999 in Lanzhou city and Jingyuan county were analyzed. The Hurst exponents of all the elements are beyond 0.5, which indicates that all the elements have evident Hurst phenomena. The results show that climate changes in Lanzhou city have a trend component, i. e. urban climate was warming up continually in the past 49 years. (3) In general, the Hurst exponents in winter and annual mean are much larger than those in summer, which indicates that the urbanization effects on climate are more powerful in winter than that in summer. (4) The Hurst exponents of different climate elements are sorted descendingly as：H (sunshine percentage), H (temperature), H (relative humidity), H (water vapour pressure), which indicates that with the limitation of meteorological and landform condition, the developments of industry and economy have much stronger influence on sunshine and temperature than that on humidity and water vapour pressure.

Key words: R/S analysis, urban climate change, Lanzhou City