Building roof garden can widen the green area and expand the green space effectively.It has the ecological function for improving the environment, beautification function for molding a person's sentiment and colorful practical function. It can promote the ecological balance of the city and optimize the environment for human residence to meet the needs of people to approach the nature and return to the nature. In designing roof garden, the favorite factors, such as wide field of vision, good illumination, large temperature difference, little pollution, small people flow as well as adverse factors concerning the field, bearing capacity, soil and wind power should be taken into account. In the meantime, to create an outer ecological space with abundant cultural connotation, it is necessary to take safety as prerequisite, ecology as basis,artistic quality as its core, function as its purpose and economy as its guarantee.