Mechanism of the initial reactions of chlorine trifluoride oxide (ClF3O) and aluminum based composite fuel was investigated using density functional theory (DFT) at B3PW91 /6-311++G (d,p) level and experimental methods. The composite fuel mainly contained isopropyl nitrate (1PN), hexogen (RDX), ammonium perchlorate (AP), n-decane, paraffin and aluminum powder. The results showed that ClF3O reacted exothermically with IPN, RDX, and hydrocarbons (n-decane and paraffin) via electrophilic substitution. The equatorial F atom was the reactive site of ClF3O. The reactive sites of IPN, RDX and hydrocarbon were different C H bonds according to the results of dual descriptor index. Reactivity of the composite fuel components was in the sequence of n-decane approximate to paraffin > RDX > IPN AP according to the energy barriers. The value of released energy from the reaction of ClF3O with n-decane was greater than 400 kJ/mol, resulting in thermal decomposition of the composite fuel. The results from XPS indicated that the composite fuel was wrapped by hydrocarbons. ClF3O reacted with hydrocarbon first and then initialized the combustion of the composite fuel in the presence of oxygen. The emission spectrum of the composite fuel combustion was studied using an intensified CCD camera. Five characteristic radical intermediates (CH, C-2, OH, NO and AlO) were determined. (C) 2018 Elsevier Ltd. All rights reserved.