In this paper, a new method, which considers random occurrence and time-space nonuniformi-ty of earthquakes, and different intensity declining shapes, is used to estimate the seismic intensity that Chengdu City will suffer in coming 50 years. First, the potential sources with different upper magnitudes are zoned by combining the pattern-recognition with subjective judgement according to the features of seismology, geophysics and seismicity. Second, the b value, and seismic frequency in potential zones, and nonuniform parameters of earthquake distribution are determined by seismicity analysis in history. Third. the equivalent round, ellipse, long ellipse and fault-rupture intensity declining models which are available in western Sichuan are set up in consideration of earthquake tectonics and isoseismal shapes. At last, a simplified method for calculating probability, which considers earthquake time-space nonuniformity, is suggested to estimate the possibility of intensity from Ⅳ to Ⅸ. The assessment will provide scientific basis for earthquake resistant project in the City.