The present invention discloses a loading unit assembly used for a linear surgical stapler, which includes a staple cartridge frame and a knife driver beam. The knife driver beam has a movable safety block defined on a surface of a proximal end thereof, and a protrusion is correspondingly defined on the staple cartridge frame. When the loading unit assembly is at its initial position, A front surface at a distal end of the safety block engages with the protrusion to stop a movement of the knife driver beam and the safety block. When the loading unit assembly is at its working position, the safety block is relatively separated from the protrusion. The present application has main beneficial effects such as: providing a safety member in the loading unit assembly, to prevent a mistake firing of the loading unit assembly when the firing ejector rod moves forwardly if the loading unit assembly is not fully assemble to its place or the loading unit assembly is forced by an outer force in a long-distance transportation And the structure is simple, effective and very practical.
