The invention provides a portal frame assembly of an independent-tool-setting type numerical control carving machine. The portal frame assembly is reasonable in load distribution, high in X-direction driving precision and long in service life. The portal frame assembly comprises a gantry, wherein the cross section of the gantry is rectangular. An X-direction perpendicular guide rail is arranged on the perpendicular surface of the gantry in the length direction, and an X-direction horizontal guide rail is arranged on the horizontal surface. Multiple carving head supporting plates are movably arranged on the gantry through the X-direction perpendicular guide rail and the X-direction horizontal guide rail, and each carving head supporting plate is formed by connecting a transverse plate and a vertical plate. The X-direction perpendicular guide rail is movably connected with the inner sides of the vertical plates of the carving head supporting plates through a guide rail pair, and the X-direction horizontal guide rail is movably connected with the lower sides of the transverse plates of the carving head supporting plates through a guide rail pair. The portal frame assembly further comprises an X-direction drive device connected with at least one of carving head supporting plate. An X-direction connecting rod is arranged among the carving head supporting plates.