The cardigan sweater is the same before and after splitting, and the number of stitches on the front and back are the same. The front piece is divided into two parts, and the back piece is one part. Next, weave first and then the film. At the beginning of the back knitting, the left and right underarms are knitting to the front by one stitch each. Then knit a needle on the reverse side, knit to the front side, and close a needle on each side under the armpits. A total of 2 stitches were collected on the left and right armpits.