A circular weft knitting machine top cylinder transmission and positioning device comprises an ascending and descending sleeve and a top cylinder transmission base, the ascending and descending sleeve is fixed on a fixed base, and the utility model is characterized in that: a radial rolling bearing is arranged between the ascending and descending sleeve and the top cylinder transmission base. As the utility model adopts the radial baring transmission and positioning with the high concentricity precision, the processing precision and the assembly precision of parts can be both greatly reduced without the single unit single matching and grinding; furthermore, a top needle cap transmission base is pointed at the center automatically, thus ensuring the requirements of the concentricity of the needle cap and the cylinder, and greatly improving the working efficiency of the whole machine and the quality of the grey fabric.