The invention discloses a lengthening and shortening vertical wall-building marker post which is a market post for building a wall. The lengthening and shortening vertical wall-building marker post comprises sections of rectangular square cylinders and is characterized by being lengthened and shortened as well as carried conveniently. The lengthening and shortening vertical wall-building marker post is provided with a section of vertical square cylinder (a beam is arranged in the vertical square cylinder and a soft wire is hung under the beam, a sash weight is hung under the soft wire and provided with a lambdoidal long strip, when the sash weight is balanced and the lambdoidal long strip on the sash weight points at a standard point on the vertical square cylinder, the vertical square cylinder is vertical). The rectangular square cylinders connected to the vertical square cylinder are also straight. Therefore, the lengthening and shortening vertical wall-building marker post is straight, and a wall vertically-built along the marker post is also vertical.