In this article, the response of thermal hydraulics parameters of the VVER-1000 is conveyed during transient condition, with different reactivity insertion. Required power distribution are computed by the MCNPX2.6 code based on the neutronic calculations, and then is coupled with COBRA-EN code. Thermal hydraulics parameters of the core, such as maximum and average fuel temperature, enthalpy, void fraction, coolant temperature and density, coolant mass flow rate, and pressure drop using EPRI model, are calculated for a steady state condition and four transient conditions of different reactivity insertion. Those conditions are related to control rod ejection accident with different worth that are 0.45, 0.47, 0.6, and 0.9 dollars in initial power of 104%, 71%, 54%, and 1%, respectively. Then results are compared with thermal limitations of the reactor core. Thermal hydraulics parameters of the core hot channel are also surveyed during this transient conditions and temperature, enthalpy, critical heat flux and minimum departure from nucleate boiling (MDNBR) of the hottest core channel are studied. Copyright (C) 2016, Hydrogen Energy Publications, LLC. Published by Elsevier Ltd. All rights reserved.