In order to achieve the fine classification of different suspicious substances in onsite rapid security inspection, this paper discusses an idea to obtain the density of substances by means of Xray backscattering signal, and completes the design and functional verification of a linear scintillator detector based on silicon photomultiplier (SiPM), which is the core component to realize the proposed method. The detector has energy resolution ability and is able to analyze the scattering attenuation of different substances under different energies. The output pulse amplitude of the detector is stable under the ambient temperature of -10℃ to 50℃, and the energy resolution varies from 221% to 257% (the energy resolution is 236% @ 595 KeV at room temperature). The structure of the linear array lays a foundation for realizing spatial onetoone correspondence between scattering and perspective images, and then hopefully realizing the fusion of scattering and perspective information. The test results of scattering energy spectra of different substances show that the energy curve detected with the detector can reflect the density characteristics of the substances, which verifies the feasibility of using the detector to measure scattering energy spectrum and achieve substance classification. The detector designed in this paper has great application prospect in intelligent identification of spot investigation equipment.