High efficiency is one of the remarkable advantages for the technology of high temperature steam electrolysis (HTSE). But when HTSE is coupled with different types of nuclear reactors, the coupled modes and materials selection of SOEC must be considered in order to achieve high overall thermal-to-hydrogen conversion efficiency. In this paper, we proposed two possible coupled modes between HTSE systems and the nuclear reactors. As for the nuclear reactor with high outlet temperature, the direct-coupled mode is a suitable choice while for the nuclear reactor with the outlet temperature of reactor lower than 650 degrees C an assistant electricity-heating mode could be adopted. To compare the overall thermal-to-hydrogen conversion efficiencies of two coupled modes, the simple energy flow charts for the water splitting cycle were presented and discussed. Also, the eta(overall) of HTSE coupled with different nuclear reactors were calculated. The results showed that HTSE should be a competitive way for large-scale hydrogen production no matter coupled with nuclear reactors with high outlet temperature or low outlet temperature. Crown Copyright (c) 2012, Hydrogen Energy Publications, LLC. Published by Elsevier Ltd. All rights reserved.