为探讨盖挖逆作法结构设计的要点和难点，以北京地铁8号线中国美术馆站西北外挂厅设计为例，介绍了盖挖逆作法结构的适用条件。通过对盖挖顺作和逆作2种方案进行比选，确定了逆作的设计方案；阐述了设计思路和要点、结构计算以及防水等关键节点的处理，并对钢管柱柱下基础形式、顶板与边桩冠梁的连接方式进行了比选、论证；最终采用暗挖小导洞内施作底纵梁作为钢管柱柱下条形基础，顶板与边桩冠梁采用固接方式连接，解决了施工用地紧张的难题，保证了周边建筑的安全。

In this paper, the application condition of cutandcover topdown construction method is presented, with the design of the outhung hall of China Art Gallery Station of Line 8 of Beijing Metro as an example. Comparison and contrast is made between cutandcover topdown construction method and cutandcover bottomup construction method and the former is adopted for the outhung hall structure. The design idea and key design points, structural calculation and waterproofing technology of the outhung hall structure are presented. The types of the foundations under the steel pipe columns and the modes of the connection between roof slabs and side pile top beams are discussed. In the end, longitudinal bottom beams constructed in mined pilot tunnel are adopted as the strip foundation under the steel pipe columns, and fixed connection is adopted between roof slabs and side pile top beams. In this way, the problem of limited space is solved and the safety of the surrounding buildings is guaranteed. 