D-shaped double cladding (DC) Nd3+-doped phosphate glass fiber with the core diameter of 20 μm is fabricated by the stacking technique and pumped by a commercial 793 nm laser diode. The maximum output power of 2.52 W at 1053 nm is generated, with the slope efficiency of 41.5% respects to the absorbed pump power. To investigate the effect of inner cladding on fiber laser performance, hexagonal, eccentric and circular DC fibers are fabricated and analyzed with the same procedure as the D-shaped fiber. The results show that among all the DC fibers with different inner claddings, the D-shaped fiber has the highest pumping power absorption, which is beneficial to improve the fiber laser performance.