Temporary bridges with modular structures are utilized permanently in many developing countries, and many have shown deterioration and damage. In addition, the problem with their permanent service is that a specific method for maintenance and management has yet to be established. Hence, it is crucial to develop a basic understanding of their design philosophy and load-carrying capacity. In a previous study, full-scale load testing was conducted on a modular-type temporary bridge in Japan to understand its actual behaviors using several sensors. This study aims to understand the critical points in maintaining those modular bridges from a structural point of view. A finite element model was developed based on the assembling manual for one of those bridges with modular structure, the Bailey bridge, and the stress conditions for each assembly type under the preset load defined in the manual were analyzed. In this study, three forms of assembly, “Single-single,” “Double-single,” and “Triple-single,” are objected to be examined in detail. One of the characteristics of modular temporary bridges is that the preset live load depends on the length of a span and the type of structure. The analysis of the models under vehicle loads shows that the maximum compressive stress is found on the top chord in the middle. The results show that the compressive stresses at the switch points of the reinforcement members vary greatly depending on the number of reinforcement members added, and reinforcing more than half of the main panels is found to be effective in reducing the compressive stress acting on the switching section. The results of the finite element modeling and analysis of the modular bridges showed the differences in stress distributions among the different types of structures.