Dual-energy computer tomography (CT) or spectral CT can obtain the equivalent atomic number of materials, which is very important for the composition detection and production process improvement of energetic materials. However, the existing methods have some disadvantages, such as high complexity, high equipment requirements. In order to improve the measurement accuracy of equivalent atomic numbers, and reduce the equipment requirements and algorithm complexity, a simple method based on the new CdTe photon counting detector is proposed to obtain the equivalent atomic number of materials. In this method, the relationship between the linear attenuation coefficient ratio in two energy bins and the equivalent atomic number is re-deduced using the attenuation characteristics of materials. This method does not rely on the professional knowledge of dual-energy CT or spectral CT. Only the photon-counting detector is used to scan and reconstruct the spectral CT of three known materials, the calibration curve of the equivalent atomic number can be obtained, and the equivalent atomic number of unknown materials can be measured. In practical application, as long as the calibration experiment and measurement experiment are carried out under the same scanning conditions, the influencing factors such as reconstruction errors, detector response errors, beam hardening effects, and scattering effects can be included in the calibration curve (equivalent to re re-calibrating the National Institute of Standards and Technology data under specific scanning conditions), and the influence of above factors on the final result can be restrained. Compared with other methods, this method is more robust and versatile and greatly reduces equipment requirements and algorithm complexity. At the same time, energy bins allowed by this method are relatively wide, which can make full use of the photons emitted by the detector. Therefore, this method makes the detection efficiency meet the needs of industrial detection and medical imaging and has a good commercial application prospect. The experimental results show that relative errors of equivalent atomic numbers measured by this method are less than 2% and have high reliability under current calibration ranges (equivalent atomic number 6~13) and scanning conditions. In the actual production detection of energetic materials, this method effectively judged the high-attenuation impurities without destroying the energetic materials. It is pointed out that the high-attenuation impurities are high-atomic number impurities mixed in the actual production process, rather than high-density concentrated energetic materials. This shows that this method can effectively solve the problem of composition detection in the actual production and testing of energetic materials and is expected to promote the improvement of the energetic material production process, which has great engineering significance.