In order to control the combustion phase precisely and remarkably extend the operation range of Homogeneous Charge Compression Ignition (HCCI) engine, a method of on-board controllable phase fuel reformation in the reforming chamber is proposed in this paper. HCCI combustion is dominated by chemical kinetics, and H-2, OH, H and O are the key radicals and play an important role in controlling HCCI combustion. The attempt of the proposed method is to try to change the control of chemical kinetics into a manipulation of fuel reforming system. The system includes an independent reformation chamber with an injector and a controllable valve that connects reformation chamber and the main chamber. The reforming fuel is reformed into H-2-rich gas. The reformed gas enters the cylinder to change the combustion phasing at compression stroke. The model of HCCI with reforming process is built with CHEMKIN 4.1 software, and HCCI process with on-board reformation is simulated. The results show that the components of the reformed gas are influenced by initial temperature and reforming mixture concentration. The maximum fraction of H-2 may be obtained by optimizing the trap timing and reforming mixture concentration (optimal value: Phi(T) = 31 degrees CA, lambda(3) = 0.4). The optimized reformed gas does have the ability to change the combustion phasing of HCCI engine. With the help of the on-board controllable phase fuel reformation system, HCCI combustion process can be precisely controlled, and the HCCI engine is allowed to operate under lower intake temperature and higher speed condition, and to keep high IMEP and indicated thermal efficiency. Copyright (C) 2011, Hydrogen Energy Publications, LLC. Published by Elsevier Ltd. All rights reserved.