The invention discloses a force-limiting assembly method and device for a turbofan aero-engine lubricating oil system component. The device comprises a fixing base, annular grooves (2), spline grooves(3) and a connecting base, wherein a plurality of connecting assembly holes (1) are formed in the connecting end face of the fixing base; the positions of the connecting assembly holes (1) correspondto the positions of assembly holes (5) in the component in a one-to-one manner; the annular grooves (2) are positioned in the connecting end face; the depth of the annular grooves (2) is larger thanthe height of a boss (6); the spline grooves (3) are formed in the annular grooves (2); the connecting base is connected with the lower end of the fixing base; and a plurality of fixing holes (4) areformed in the bottom face of the connecting base in the circumferential direction. The force-limiting assembly method and device solve the problems that the degree of freedom of the component is limited, and deformation is likely to happen, an accurate and efficient assembly manner is provided, and the work efficiency is improved.