In this paper, three simplification plans for the zinc-sulfur-iodine thermochemical cycle are designed, namely the open-loop system, the five-step cycle, and the electrochemical cycle. Parameters for each simplified cycle are presented. Thermal efficiency is regarded as the evaluation criterion of the whole system, and thermal balance for each cycle is investigated. Results show that the variation of thermal load for the whole system is the primary reason for changes in thermal efficiency. Thermal efficiency of the open-loop system is improved to 57% under proper operating conditions, and concentrated H2SO4 with a mass fraction of 92.5 wt% is output. As for the electrochemical cycle, its thermal efficiency almost keeps the same with the original one, since study on its critical factor, the electrochemical Bunsen reaction, is not enough. What's more, chemical processes of the five-step and electrochemical cycle are simplified drastically by comparing to the original one. (C) Copyright 2015, Hydrogen Energy Publications, LLC. Published by Elsevier Ltd. All rights reserved.