Abstract: The long-span steel structures are developing quickly in recent decades around the world.Although few problems appeared in ordinary steel structures,many problems were met during the erection process of the long-span steel structures,such as the strength,stiffness,stability in large scale truss erection procedure,the interaction between permanent structures and temporary structures in the removing procedure.The construction mechanic method can be used to select and guide the construction of long-span steel structures,and can be used to real-time analysis by comparing to the monitoring data which guarantees the construction safety.An analysis method for tracing construction process is developed,which can be built on FEM platform such as ANSYS,MARC etc.It can be used to consider the influences of construction loading,supporting conditions changing,members adding and removing etc.