The present invention relates to a method and spinning device for drafting single yarns. The method comprises drafting fiber strands into twistless fiber strands, bringing a primary twist action upon fiber strands in the vortex twist zone, integrating and compressing fiber strands on the suction member to form column fiber strands, outputting column fiber strands and twisting them into spun yarns. The spinning device comprises a drafting mechanism with suction members, wherein the front drafting pair consists of a front rubber roller, a block rubber roller, and a suction member, an air guide member is installed on the suction member, and the block rubber roller, air guide member, and the suction member jointly form a vortex twist zone which fiber strands can pass through.