The influence of various types of index profiles on the characteristics of power transmission, including the effective mode area (Aeff) and the maximum power density (Dmax) in the cross section, is investigated. A unique expression for the index profile, which is appropriate to the most practical index distributions of optical fibers, is employed in the calculation of Aeff and Dmax with the comparison of the step index profile. The simulation result indicates that under the condition of equal transmission power and the difference of the mode effective index (Δneff) larger than 10-4, the index profile with a center dip will effectively lead to the reduction of Dmax and the increase of Aeff. This research provides theoretical basis for the design and fabrication of passive large core fiber for large power transmission.