A cap plate welding assembly for an electric vehicle secondary battery provided with an anode part and a cathode part fixedly inserted on an upper surface thereof and coupled to an upper part of a battery pack casing for the electric vehicle secondary battery, the cap plate welding assembly for an electric vehicle secondary battery, comprising: an anode part cap plate formed long in left and right directions in a shape of a square plate material; and a cathode part cap plate formed in the same size as the anode part cap plate and having one side surface thereof coupled by welding to an opposite side surface of the anode part cap plate, wherein the anode part cap plate is provided with first horizontal planes formed long in the left and right directions on a front surface and a rear surface thereof, respectively, and first vertical planes perpendicular to the first horizontal planes and formed in front and rear directions on a left side surface and a right side surface thereof, respectively, wherein the cathode part cap plate is provided with second horizontal planes having the same shape and size as the first horizontal planes and formed long in the left and right directions on a front surface and a rear surface thereof, respectively, and second vertical planes having the same shape and size as the first vertical planes and formed in the front and rear directions on a left side surface and a right side surface thereof, respectively, wherein the first vertical planes include one first vertical plane coupled by welding to associated one second vertical plane of the second vertical planes, the associated one second vertical plane being opposite to the one first vertical plane, and wherein the anode part cap plate is provided with a first seating part, on which a lower portion of the anode part is seatable, and which is recessed to be formed on a right side of an upper surface thereof, wherein the cathode part cap plate is provided with a second seating part, on which a lower portion of the cathode part is seatable, and which is recessed to be formed on a left side of an upper surface thereof, and wherein coupling by welding is performed between the first vertical plane most distant from the first seating part of the anode part cap plate and the second vertical plane most distant from the second seating part of the cathode part cap plate. an anode part cap plate formed long in left and right directions in a shape of a square plate material; and a cathode part cap plate formed in the same size as the anode part cap plate and having one side surface thereof coupled by welding to an opposite side surface of the anode part cap plate, wherein the anode part cap plate is provided with first horizontal planes formed long in the left and right directions on a front surface and a rear surface thereof, respectively, and first vertical planes perpendicular to the first horizontal planes and formed in front and rear directions on a left side surface and a right side surface thereof, respectively, wherein the cathode part cap plate is provided with second horizontal planes having the same shape and size as the first horizontal planes and formed long in the left and right directions on a front surface and a rear surface thereof, respectively, and second vertical planes having the same shape and size as the first vertical planes and formed in the front and rear directions on a left side surface and a right side surface thereof, respectively, wherein the first vertical planes include one first vertical plane coupled by welding to associated one second vertical plane of the second vertical planes, the associated one second vertical plane being opposite to the one first vertical plane, and wherein the anode part cap plate is provided with a first seating part, on which a lower portion of the anode part is seatable, and which is recessed to be formed on a right side of an upper surface thereof, wherein the cathode part cap plate is provided with a second seating part, on which a lower portion of the cathode part is seatable, and which is recessed to be formed on a left side of an upper surface thereof, and wherein coupling by welding is performed between the first vertical plane most distant from the first seating part of the anode part cap plate and the second vertical plane most distant from the second seating part of the cathode part cap plate.