An experiment of sixteen frame column underpinning joints of frame structure moving was introduced, the experiment sample failure phenomena and failure type was obtained. The type was like “deep beam” failure type-“tension bar arch”, and the last failure place occurred on the interface of column and beam. Then, the underpinning joint stress mechanism and failure mode was determined based on the experiment’s conclusion. In addition, the failure course of joint was divided two stages which were before and after interface punching slip by theoretical analysis, for the stage before interface punching slip a space “tension-bar-arch” mechanical model was presented for the underpinning joint, then theoretical bearing capacity equation for this underpinning joint were obtained. At the same time, for the stage of interface after punching slip, the theory of interface shear was put into the analysis of joint, then interface bearing capacity equation was obtained for this stage. At last the height equation was obtained by the analysis of the stage of after interface slip.