In order to study the heat, stress and deformation in the process of laser coaxial powder feeding additive connections of large component, and to explore their distribution laws and evolution characteristics, ANSYS parametric design language is used to realize the finite element numerical simulation of the connecting processes through programming. Results show that the proportion of the joint area is small so that the heat affected zone will be concentrated around the joints. When the distance between the joints is close, the heat affected zone will be overlapped. The stresses at the joints have different characteristics in the connection stage and cooling stage. The stress values are not high, and the stress concentration is not obvious during connecting. At the initial stage of cooling, the stresses increase and at the same time tend to be concentrated. After a period of time, the stress will be stable at the high position, and the concentrated high stress zones will be formed at the joints. Under the boundary conditions, the longitudinal warpage of the frame is obvious, and the shape error will occur after the cylindrical hole is connected. Because there is only the deformation compatibility between the roots and the frame, the rib plates deflect in different directions and angles. The connection positions and constraint modes have great influence on the forming accuracy.