A sewing machine accessory includes a plate for attaching to a sewing machine workbed and to be located below a needle, the plate includes an opening and a guiding track, and a positioning device includes a sliding member slidably engaged with the guiding track of the accessory plate, and a pointed member extended from the sliding member for engaging with a cloth material to be stitched and for forming of an arced stitch on the cloth material, and the pointed member is movable close to the needle for stitching or forming a circular or arced stitch that includes a relatively decreased or smaller outer diameter.