A manufacturing method of a mulching sheet is provided to supply moisture and air to soil smoothly by improving permeability of air and water through a minute cell. A manufacturing method of a mulching sheet comprises following steps. The first mixture formed by mixing raw material(foaming agent, and calcium carbonate) of powder or pellet form is injected into an input part of a first extruder. The second mixture formed by mixing raw material(calcium carbonate) of powder or pellet form is injected into an input part of a second extruder. The second mixture formed by mixing raw material(calcium carbonate) of powder or pellet form is injected into an input part of a third extruder. The first mixture and the second mixture are blow-formed through one outlet at the same time. The first mixture is poisoned and on the external side of the blow molded product and the second mixtures are successively positioned on the middle side and the internal side. The cross section of the blow molded product is cut and the cut blow molded product is wound in a branch pipe to be spread in a sheet form.