Abstract: Some early-built steel truss bridges can no longer meet the requirements of current traffic capacity, so it is necessary to reinforce the main trusses of the original bridges. Bridge reinforcement is usually carried out under load. It is necessary to consider the phased forces of the reinforcement members. The different degrees of unloading corresponding to different reinforcement construction schemes will produce different reinforcement effects. In this paper, based on the reinforcement and reconstruction project of the Songpu Bridge, the element birth and death technology of ANSYS is used to simulate the strengthening construction process. A finite element simulation method considering the strain lag of the reinforced plates is proposed. The stress distributions of the old and new members under three different reinforcement schemes corresponding to different degrees of unloading are calculated. The influence of unloading degrees on the reinforcement effect is analyzed in terms of component safety and material utilization efficiency. The comparison and selection of construction schemes are carried out considering the social impact. The results demonstrate that the proposed component reinforcement simulation method can effectively consider the strain lag effect and is convenient to simulate the reinforcement of truss members. Safety degrees of reinforced members and utilization ratios of reinforced materials increase with the increase of the unloading degree. Considering the social impact, it is recommended to adopt the construction scheme which replaces the lower deck first, removes the upper deck, then reinforces the main truss structure and finally installs a new upper deck.