The invention provides a folding method of a square box with an inclined opening and relates to a manufacture method of a paper utensil. The square box with the inclined opening is formed by a high assembly and a low assembly. A folding method of the high assembly comprises the steps of taking out a piece of square paper, making a folding line, folding a part above a first transverse folding line downward, and folding a part below a second transverse front folding line upward. A folding method of the low assembly includes the steps of taking a piece of rectangle paper which is horizontally long and longitudinally short, wherein the rectangle paper and the square paper are equal in side length and a length-to-width ratio of the rectangle paper is 3:2, folding a part above a fourth transverse folding line downward, and folding a part below a third transverse folding line upward. Two ends of the low assembly are inserted into inter-layers of two ends of the high assembly to form a cube, and the cube is folded and evened according to the folding line of the short side of the lower portion, a first diagonal line right folding line (5) and a second diagonal line right folding line (6) to form the square box with the inclined opening. The folding method of the square box with the inclined opening breaks through a tradition of square boxes with flat openings, is novel in mould, attractive, elegant, simple in manufacture method, and easy to operate, and creates imaginative and large creation space for people.