The invention claims a waterproof and oil-proof agent prepared by using fluorocarbon grated starch. The preparation method of the waterproof and oil-proof agent comprises the following steps of: using the starch as the raw material, pasting the starch and initiating the starch by a free-radial initiator; in the emulsion system, polymerizing and grating the fluorine-containing monomer and the starch for 3 to 10 hours at the constant polymerization temperature of 40 to 95 DEG C. The waterproof and oil-proof agent of the invention can be applied to the pulp and paper making process, improves theretention rate of the small fibres when being added to the inner wet part of the paper pulp and improves the smoothness of the paper surface when being coated on the paper surface. The invention alsocan be applied to the textile and is used for the sizing material, the thickening agent for printing and dyeing, and the finishing agent of textile.