An automatic packing machine and automatic packing method for express delivery are provided. The automatic packing machine for express delivery includes: a frame; a box discharging mechanism, fixed to the frame; a weighing mechanism, fixed to the frame, the weighing mechanism including a weighing plate and a weighing plate steering engine which are arranged in coordination and an image collecting module, the weighing plate steering engine and the image collecting module being fixed to the frame, and the image collecting module facing the weighing plate; a box body unfolding mechanism; a box closing mechanism; a conveying mechanism; and a controller, connected to all other structures of the automatic packing machine for express delivery. Through the technical solutions of the present invention, multiple functions are integrated, the degree of automation is high, and different items are packaged by using different box bodies.