A production method of bicycle seat cushion body comprises the steps of: firstly sucking a surface layer in a mold cavity of a forming mold by vacuum suction, so that the surface layer has a main zone pasted on an inner wall of the mold cavity and a periphery zone surrounding the main zone, then heating a substrate in the mold cavity of the forming mold to form a flexible body, so that the main zone of the surface layer is perfectly combined with the flexible body, combining a bottom case to the flexible body, and finally backward folding and fastening the periphery of the surface layer to the bottom of the bottom case. Accordingly, the production method of bicycle seat cushion body can avoid the problems of non-uniform force received on the surface layer, pasting on the flexible body not perfectly, and non-smoothness at the edge of the main body of the seat cushion, thereby simplifying the manufacture procedure of the main body of the seat cushion.