The engineering geological condition, pit support design and its construction process in Beijing Century Building Project are mainly introduced in this article. It is narrow around the deep and big pit. It is designed via calculation and contrast that the top wall with nail in soil plus the bottom slope-supporting pile is adopted on the narrow west pit near a road and existing buildings and that the top wall with nail in soil plus the bottom slope-supporting pile and anchor is used on the rest parts of the pit. This scheme has excellently solved the problem of the low security and has relatively reduced the cost of the support and protection of the pit. This article has some reference sense to the design and construction of the deep and big pit.