Many shipowners choose to install the desulfurization system on ships as the approach of the entry into force of MARPOL Convention that sets limits on SO _X emissions from the ship exhausts in the global maritime space. Based on the project of a large crude oil tanker with the retrofitted desulfurization system, the power system after the transformation has been analyzed and studied. This project decide to add a desulfurization generator and a switchboard for the desulfurization system, in order to meet the requirements of the shipowner for the fuel economy of the ships during navigation. It can be seen that this scheme is not only feasible, but also can maximize the integrity of the original power system through the load estimation, short-circuit current calculation and alternative analysis of the power system.