The invention relates to a knitting mechanism for a flat knitting machine and a method. The knitting mechanism comprises a triangular bottom plate and a knitting needle assembly. At least one knittingunit is arranged on the triangular bottom plate, the knitting unit and the knitting assembly cooperate to carry out knitting, the knitting unit comprises an upper left protection plate, a swing cam,a needle turnover cam, an upper right protection plate, a left stitch cam, a right stitch cam, a knitting cam, a disc assembly, a guide assembly corner, a non-woven pressing sheet and a needle selecting cam. A needle groove is formed in a needle plate body, combined knitting needles are arranged in the needle groove, and the combined knitting needles comprise a retreating needle, a long stitch, ashort stitch and a needle selecting stitch. The needle selecting triangular structure design is simple, processing is easy, and the needle selecting position is accurate. Compared with an existing bottom plate device, the bottom plate structure is more simplified, the weight is reduced, the long stitch is only provided with a needling butt, the structure is simple, five basic actions of knitting,ring gathering and needle turnover and non-weaving can be carried out, and a specific needling knitting method is provided.