The strain calculation for equal-channel angular extrusion provides the basis data to grasp the deformation degree,to measure effect of the severe plastic deformation,to formulate the technical regulation and to design the forming die. In the field of severe plastic deformation at home and abroad,the widely adopted formula for strain calculation was put forward by Iwahashi Y in 1996 is widely adopted. However,after analysis,faults about this formula were pointed out: analyses of the effect of tangential vel...