The invention discloses an instrument assembly for implanting a revision hip prosthesis. A surgical instrument assembly for implanting an orghopedic hip prosthesis during a surgical procedure. The assembly comprises a test shaft having a cylindrical rod, a locking screw and a locking mechanism; the locking screw is provided with multiple screw threads formed in a distal end, and the locking screw can be rotated relatively to the cylindrical rod; a discrete test neck, which is detachably fixed to the test shaft; the test neck is provided with bore formed in the neck, wherein the rod of the test shaft is contained inthe bore hole so as to allow rotation of the test neck relative to the test shaft; the locking mechansim can be operated in order to selectively lock the rotation position of the test neck rod relative to the test shaft.