Two types of tubular dielectric elastomers (DE) torsional actuators are studied in this work, which are respectively reinforced by a family and two families of helical inextensible fibers. When subject to a radial electric field, torsional deformation will be induced in the DE actuators due to the constraint of inextensible fibers. By conducting finite deformation analysis with the principal axis approach and adopting appropriate constitutive equations, simple analytical solutions are obtained for the considered DE actuators. Furthermore, the effects of material parameters and the fiber angles as well as externally applied axial force and twist moment on the voltage-induced torsional behaviors of the two DE actuators are discussed in order to explore their maximum torsional actuation capability. The concept design presented here provides an effective approach for achieving large torsional deformation, and the developed model and revealed results will aid the design and fabrication of soft actuators and soft robots.