The invention relates to a biodegradation thin film which takes poly (propylene carbonate) as matrix and a preparation method thereof. The thin film takes biodegradation poly (propylene carbonate) as matrix and is blended with biodegradation polyester and an auxiliary agent which can be in contact with food directly to prepare a special material for blown film. If a blown film is produced by common blown film equipment, the mechanical property of the film is close to that of linear low density polyethylene. The tensile strength and the elongation at break of the biodegradation thin film provided by the invention can respectively reach as high as 37MPa and 680 percent; and the tensile strength and the elongation at break of the linear low density polyethylene sold on markets are respectively 30MPa and 710 percent.