The invention discloses a fixing mechanism used for chemical petroleum pipeline machining. The fixing mechanism comprises a base, a sliding groove is formed in the top of the base, two sliding blocksare arranged in the sliding groove and can move in the sliding groove, a clamping plate is arranged at the tops of the sliding blocks, a stand column is further arranged at the top of the base and isprovided with a movement block, the stand column is sleeved with the movement block, the movement block can move in the axis direction of the stand column, two transverse rods are arranged on the sideface of the movement block and are located on the two sides of the axis of the movement block, a transverse plate is further arranged between the two transverse rods and can move on the transverse rods in the horizontal direction, a through hole is further formed in the top of the transverse plate, and clamping elements are arranged on the two sides of the through hole. By means of the fixing mechanism, a petroleum pipeline bend can be stably fixed, and swing during machining is guaranteed.