It is devoted to study the physical feasibility of nondestructively detecting and identifying fissile material or concerned nuclear device.The key point of the technique is to measure characteristic γ radiation emitted spontaneously from the nuclear fissile material,and to extract the useful information of nuclear fissile materials to be measured.By using simulated γ-spectra data,this method is tested and the results show that the isotopic composition and other characteristic information can be extracted from the measured γ-ray spectrum of fissile materials with accuracy better than 2%.Also,it is indicated by this study that the geometric self-shielding correction (the γ-ray self-absorption)of the measured fissile materials is one of the key factors to improve the accuracy of calculations.And simplified semi-empirical expressions are also presented for the self-shielding correction factors of certain simple geometric configurations.The mathod discussed applies to the nuclear material safeguard techniques such as monitor,verifying and account etc.