The reaction of nano-aluminum (nAl) and water (H2O) is regarded as the main ingredient of the new generation of underwater propulsion system. In this paper, a novel in-situ investigation method was introduced, and the reaction characteristics of nAl and H2O in different mole ratios were detailed analyzed. By monitoring the variation of real-time temperature with heating time, three characteristic temperature points and three significant evaluation parameters in the reaction process were extracted from the T-t curve and (dT/dt)-t curve, where the T and (dT/dt) were the real-time temperature and its first-order differential, respectively. The characteristic temperature points could be applied to divide the entire process of the reaction, while the evaluation parameters could be applied to evaluate the performance of nAl/H2O system. Based on the proposed method, it was found that the best mole ratio interval of reactants in nAl/H2O reaction system was between 1:2 and 1:2.2. Furthermore, the specific reaction process of nAl/H2O system could be presented. (C) 2012 Elsevier B.V. All rights reserved.