Abstract: On the basis of analyzing the current situations and problems of space forms of metropolises in China，as well as the curent structure and problems of transportation in Xi'an，this paper points out the experiences of optimizing the structure in some urbans，such as in Tokyo，and discusses the leading function of rail transit for optimizing the city structure of Xi'am．

Key words: rail transit, urban structure, units structure with multi-center, organic evacuation

摘要： 分析了我国大城市的空间结构现状和存在的问题以及西安城市结构布局现状和交通存在问题，总结了东京等 大城市的结构优化经验，探讨了轨道交通对西安城市结构优化的引导作用．

关键词: 轨道交通, 城市结构, 多中心组团结构, 有机疏散