Through the analysis on components of the environment,the essential factors affecting the city illumination,such as human beings,light and objects,are discussed in this paper with the help of environment psychology.On the basis of people's visual characteristics and psychological needs,the characters of illumination of the city in whole,city square,buildings and garden landscape are summarized and the laws of city illumination are revealed.It is found that designing the city illumination should create not only a visual environment but coordination with city spatial elements and physiological sense of human beings,offering a psychological environment in harmony with function atmosphere.The author finally puts forward his thinking on city illumination which combines the natural condition,object form,people's visual characteristics and environmental features based on the environment principle.