To provide a method for simply capable of knitting a box-formed knitted fabric obtained by joining a closing surface with a final course of the side surface part of a tubular material having an even number of corner parts even if the lengths of the sides formed in the final courses of the side surfaces are different.

This box-formed knitted fabric having side surface parts and a polygonal closing surface formed as being joined with the final courses of the side surfaces is knitted as a non-sewn material by using a flat-knitting machine. This knitting method includes the following processes. A process of knitting the side surface parts as tubular by connecting the end parts of knitting width direction to each other of each of the knitted fabrics knitted by front and rear needle beds so that the each of surfaces formed between the corner parts in the side surface part is not knitted over opposing needle beds. A process of knitting a closing surface as continued from the final course of at least 1 surface of the opposing 2 surfaces in one set of sets of opposing 2 surfaces in the side surface part. A process of joining the closing surface with the final course of the surface adjacent to the surface continuing to the closing surface at the side surface part at the same time with performing the knitting of the closing surface. A process of performing a bind off treatment of the closing surfaces between each other, or performing the bind off treatment of the closing surface with the remaining final course of the side surface part.