The settlement law during the underpinning process of a frame structure was analysed using the three-dimensional finite element model based on ANSYS program. The birth and death technique was adopted to simulate the work state of the underpinning structure and the underpinned piles. The secondary settlement deformations in the process of foundation underpinning can be simulated when the settlement values of the column bases before underpinning were applied to the underpinning structure. The settlement-location curves of the frame column bases before and after underpinning can be gained through path operation. The analysis results show that the settlement values and the differential settlements of the underpinning location increase obviously after underpinning, the medial deflection of the underpinning beam increases, and the settlement value of corresponding frame becomes bigger. The deformation of the underpinning beam occupys big proportion in the total settlement deformation. When the length diminishes and the diameter augments of the underpinning pile, the stiffness of the pile increases, therefore the settlement values and the differential settlements decrease. When the span diminishes and the height augments of the underpinning beam, the stiffness of the beam increases, accordingly the settlement values and the differential settlements decrease obviously. The width change of the underpinning beam has little influence on the settlement values and the differential settlements.