In order to improve the longitudinal resolution of terahertz imaging detection, a novel longitudinal resolution enhancement method based on empirical mode decomposition of continuous wavelet was proposed. Firstly, the frequency domain signal of the sample is processed by continuous wavelet transform to obtain the corresponding continuous wavelet transform coefficients. Then, the obtained continuous wavelet coefficients are decomposed by empirical mode decomposition, which is adaptively decomposed into a series of intrinsic mode functions and a residual signal. And the first-order intrinsic mode function is extracted as the imaging parameter for 3D reconstruction to obtain the final 3D intrinsic mode function image, so as to improve the longitudinal resolution of terahertz detection image. In order to verify the effectiveness of the method, the 150 GHz~220 GHz high frequency terahertz frequency modulated radar imaging system was used to detect two kinds of sandwich structure composite material with internal adhesive debonding defects, and the proposed method was used to process them. The detection result images with the longitudinal resolution effectively enhanced and the sharpness effectively improved were obtained, which provides a new idea for future terahertz computer tomography imaging and terahertz non-destructive testing research.