Bolt connections possess significant advantages such as high load transfer capacity and reliability, making them a widely adopted method for mechanical connections in various engineering structures. The load-carrying capacity of bolted connections can be significantly influenced by factors including assembly sequence, warping of the connector, and environmental conditions. These factors may lead to loosening or over-pretightening of the bolts, resulting in deviations from the designed overall force distribution and load transfer mechanisms, potentially causing premature structural failure. In this study, progressive failure assessment was employed to investigate the bearing capacity and failure modes of bolted structures under different preload forces. Based on these findings, a nonlinear regression prediction model was established to analyze the impact of non-constant preloads on the bearing capacity of bolted structures. The research demonstrates that bolt preload has a substantial influence on the connection’s bearing capacity. Within a reasonable range, the bearing capacity increases with increasing preload. However, when the preload exceeds this optimal range, excessive preload not only reduces the bearing capacity but also causes the failure locations and modes to deviate significantly from design expectations.