In this paper cotton hollow yarns were obtained from the core spun yarns which were produced on a little modified conventional experiment ring frame with water soluble staple PVA yarn as the core. For comparison, yarns with same linear densities, same twists of the sheath, different linear densities, different twist directions of the core were prepared. The results show that the tensile strengths of the hollow yarns decrease first, then increase and decrease again, at last the tensile strength trends to reach a steady state with the soluble PVA core extraction proceeding. And when the sheath linear densities of the core spun yarns are constant, their twist and twist direction are same as that of the core it will be easier to remove the core of the yarn with a higher core size. When the linear densities of the sheath and the core are all constant, the twists of them are same,it will be easier to remove the core of the yarn with a different twist direction of core to the sheath.