RDX is a most widely used military explosive. As the development of new warheads, there are more and more applications of RDX with abnormal grain shapes. To ensure the operational effectiveness of the new warheads, it is necessary to find an on-line nondestructive methods that can measure the RDX grain’s internal pressure. In this paper, we use Raman spectrum and first-principles methods to determine the characteristic spectral line of the RDX samples and have studied the shift of the Raman spectral lines under various pressures. In particular, we measured the RDX samples under the pressures of 10, 20 and 30 MPa, respectively, and checked the fitting errors by measuring the RDX samples under the pressures of 15, 25 and 35 MPa, respectively. It is found that the shift of the characteristic Raman spectral line has a good linear dependence on the external pressures. Therefore, we can at first calibrate the linear relation between the shift of the Raman spectral line of regular RDX and the pressures in laboratory and then measure the Raman spectral line shift of the RDX with abnormal shapes. Based on the calibrated linear relation and the measurement of Raman spectra, one can determine the internal pressure in RDX. In this way, we can realize the nondestructive detection of the internal pressure of RDX. The experiment results show that this method has the advantage of good sensitivity and reproducibility. The Raman spectrum method has been successfully tested in the warhead production line.