In many developing countries, temporary bridges with modular structures, so-called Bailey bridges, are often in permanent use, and specific maintenance methods have not yet been established. In general, it is economically challenging to replace many temporary bridges in those countries. Therefore, it is necessary to clarify the evaluation methods for maintenance and structurally essential parts of bridges and to keep them in service under appropriate maintenance and management. In a previous study, stress analysis based on yield stress was conducted to determine the maximum stress and its occurrence point in each assembly type of Bailey bridge. In addition, buckling is a crucial factor to be considered in the analysis of truss bridges and should also be considered in the study of Bailey bridges. This study aims to reproduce the structurally sound condition and deterioration case of Bailey bridges of each assembly type and analytically reveal which damage form precedes the other, focusing on buckling or yielding and the points of the damage. In addition, a finite element model was used to simulate deterioration phenomena, such as missing a bolt and corrosion, to clarify the influence of the deterioration state on the load-bearing mechanism. Seven single-single patterns and eight double-single patterns were analyzed using an assembly manual. As a result, it was clarified that buckling precedes yielding in many of the assembly types and that the central upper chord of the main structure is a critical member in terms of maintenance and management because of the risk of buckling. In the case of corrosion deterioration of the central lower chord in tension, the lower chord yielding preceded the upper chord’s buckling.