This study investigates stress monitoring and calculation for discontinuous section subgrade boxes under crawler crane moving loads during construction, focusing on structural optimization and bearing capacity enhancement. To address stress concentration at subgrade box web welds, a reinforcement plate solution was proposed. Four monitoring points were installed on the east (unreinforced) and west (reinforced) sides for comparative analysis. Real-time stress data were captured via vibrating wire sensors, complemented by numerical simulations. Results showed simulation errors remained within acceptable limits, with minimal discrepancies in reinforced areas, validating the design’s efficacy. The reinforcement strategy not only mitigates localized stress but also offers a practical framework for improving subgrade box safety and operational reliability, contributing actionable insights for engineering applications.