Hybrid cable-stayed suspension (HCSS) bridges enjoy broad application prospects due to their excellent stability and economic benefits. The mechanical response of the transition section between the two subsystems of this novel bridge type is a common concern in the design and use stages. This paper took the design scheme of an HCSS bridge with a main span of 1440 m as the research object. A global finite element model (FEM) of the example bridge and local finite element models of the transition section were established, and the mechanical performance of the subsystem and components of the transition section was investigated. Moreover, parametric studies were conducted to investigate the influences of varies structural parameters on the mechanical performance of the transition sections of HCSS bridges. The results show that the mechanical behavior suddenly changes significantly at the transition between the cable-stayed section and the suspension section. Performance mutations in the transition section of a HCSS bridge can be improved by changing structural parameters, such as the transition section length, the number of cross cables, the area of the outermost cables, and the distance between the outermost cables and adjacent cables. The present findings may provide a reference for the better understandings and design of HCSS bridges.