The invention discloses a method for manufacturing a cover plate of a lithium-ion battery, which comprises the following steps: drilling two holes on the periphery of an ordinary cover plate, wherein the two holes can be arranged in a diagonal line, in parallel on one side or on opposite sides; manufacturing a gas diversion tube, wherein the upper part and the lower part of the gas diversion tube are communicated, the bottom edge of a tube body extends inwards but is not butted, a baffle is arranged on the bottom edge of the tube body and is clamped at the bottom of the tube body, a spring is welded on the baffle, and the surface of the tube body is coated with an elastic adhesive film free from reaction with electrolyte; and welding the top part of the tube body of the gas diversion tube and one end of the spring in a box on the cover plate under one hole through laser. The spring is made of a carbon steel wire material, the tube body is made of an aluminum material and is shaped like a trapezoid, and the two holes are arranged diagonally. When the method is adopted to manufacture the cover plate, the manufacturing process can be fundamentally prevented from interference of the external environmental humidity, and water generated in the process can be prevented from entering in the battery to cause flatulence and other unfavorable factors affecting the battery performance.