Abstract: The prestressed assemble steel support system (PASS) is an innovative steel support which can be recycled and prestressed and has a lot of advantages, such as high-strength connection and high reliability, so it has been used more and more in China. To solve some problems urgently, a series of PASS pressure and observation experiments are carried out in a project with large span and poor soil in the west of Hangzhou. The experiment shows that the measured stiffness of PASS is slightly less than that in theory, and the critical factor for deformation of the foundation pit is the supporting prestress. The carrying capacity of PASS depends on the stability of support, so it should meet the design requirements and has a lertain redundancy. The maximum stress of PASS varing with temperature is about 29.1% of the actual axial force or 7.4% of the design axial force, and the influences of temperature stress are controllable.