Abstract: As a national scientific engineering project, the main facility of Shanghai Synchrotron Radiation Facility (SSRF) is composed of thousands of components with large or small dimension. Many key devices of them have the requirement of sub-millimeter assembly accuracy. In design stage, the design and virtual assembly of devices were realized by mechanical software Solid Edge and Unigraphics (UG) to avoid potential interference within and among devices. After the first group of components was fabricated, several times of test assembly were carried out to find the design bugs and optimize the design, then batch production could be approved. In installation stage, precise 3D measurement instruments, such as the laser tracker and the articulated arm, were fully utilized to assure about 0.2 mm assembly accuracy between devices, and a key engineering milestone was achieved by acquiring synchrotron light ahead of the schedule about three months.