Contemporary warfare, marked by multi-force collaboration, cross-domain synergy, and dynamic multi-task interdependencies, demands advanced approaches to operational mission planning. Targeting the challenge of mission chain construction in amphibious joint air-ground landing operations, this study introduces a systematic framework grounded in the Work Breakdown Structure (WBS) methodology. By formalizing task descriptions, defining decomposition principles, and resolving task constraints and logical dependencies specific to amphibious operations, the WBS-based approach ensures alignment with systemic combat logic. Elemental task relationships are analyzed through a matrix representation, enabling the generation of executable mission sequences. Empirical validation via case studies confirms the feasibility and efficacy of the proposed method in constructing mission chains for complex amphibious joint operations.