This paper aims to research on spatial effects of events, which are valuable for establishing comprehensive performance appraisal system. The authors provide a case study of Kunming World Expo. The paper, firstly, examines the forming mechanism of spatial effects and research framework of the mega-events. And the authors point out that mega-events are the social progress implanted into urban process and their spatial effects are derived from their internal attributes of "spatial investment" and "social mobilization". And the social-spatial dialectic of the neo-Marxism is the framework for analyzing spatial effects of social process. The methodology of empirical research is adopted in this paper and the authors examine the influencing period of Kunming World Expo (1997-2003) with a quantitative analysis. Then the paper analyzes main characteristics of urban spatial evolution in Kunming during 1997-2003. The authors conclude the characteristics from the following four aspects. (1) The time series of the urban spatial evolution are advanced and the investment of urban space enters into peak season and the reconstructing of physical space is relatively advanced; (2) the Kunming World Expo leads physical space into growing at axial direction and the northeast part increases rapidly; (3) evolution of urban social space presents varying characteristics which differ from the similar cities; (4) it establishes an explaining frame of the relation between Kunming World Expo and spatial evolution. The authors believe that the World Expo influences evolution of urban space through the following aspects. (1) Creating a favorable environment of investment for spatial reconstruction in order to attract large amount of spatial investment; (2) social mobilization minimizes the cost of reconstruction of urban space, and accelerates the process of evolution of space; (3) the World Expo increases urban attractions and leads to the implant of external factors so that evolution of social space presents characteristics of external implant.