we will first discuss a generalized positive mass theorem on a class ofpiecewise smooth asymptotically flat manifolds with broken mean curvatureacross a hypersurface. then we will relate it to bartnik's quasi-localmass definition and explain how corvino's scalar curvaturedeformation theorem implies that a minimal mass extension, if exists,must be static. finally, we will prove that, for any metric thatis close enough to the euclidean metric on a ball and has reflectioninvariant boundary data, there always exists an asymptotically flat, scalar flat and static metric extension with bartnik's geometric boundarycondition.