With the continuous development of helicopter design, resin matrix composites have been widely implemented in helicopter structures. Both the ​application scope and ​percentage of material usage have significantly increased with technological advancements. The spar serving as the primary load-bearing structure of rotor blades is entirely manufactured from composite materials using multiple prepreg layers. This structural characteristic renders the curing process of spar structures particularly complex, where the multilayer composition frequently results in inadequate interlayer adhesion post-curing. This paper proposes an interference-fit assembly methodology capitalizing on the thermal expansion properties of composites, establishing an effective compaction mechanism for the layered structure. To validate this approach, numerical simulations were employed to calculate the normal pressure exerted by tooling on the prepreg layers during assembly, enabling analysis of interlayer compaction states. Furthermore, the maximum stress criterion was applied to determine whether damage occurs within the skin layers. Finally, experimental tests preliminarily validated the method's effectiveness.