The current parameterized building information model of assembled steel-concrete composite structures lacks structural information and cannot realize the modification and self-renewal of the drawings of assembled steel-concrete composite structures. Therefore, both the damage assessment effect of structural members and the seismic reinforcement performance are poor. This paper presents a building information model for seismic reinforcement of assembled steel-concrete composite structures. The model framework included a building design model, a structural design model, a seismic reinforcement design of the building, and damage assessment. Through solid definition, attribute definition, and association definition of structural members, the seismic strengthening performance information regarding the steel-concrete composite structural members, i.e., columns, beams, slabs, and walls, was comprehensively described. The accurate comprehensive damage index of structural members was obtained to evaluate the reinforcement grade of the structural members by using a fuzzy reinforcement evaluation method. The experimental results showed that the error between the damage index obtained by the proposed model and the actual damage index was < 0.03, which indicated that the accuracy of the model for seismic reinforcement of assembled steel-reinforced composite structures is relatively high.