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 signals of the sample are processed by continuous wavelet transform to obtain the corresponding continuous wavelet transforms coefficients. Then， the obtained continuous wavelet coefficients are decomposed by empirical mode decomposition， which is adaptive decomposed into a series of intrinsic mode functions and a residual signal. And the first-order intrinsic mode functions are extracted as the imaging parameter for 3D reconstruction to obtain the final 3D intrinsic mode function image， so as improving the longitudinal resolution of terahertz detection image. In order to verify the effectiveness of the method， the 150～220 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 results images of the longitudinal resolution effectively enhanced and the sharpness effectively improved was obtained， which provides a new idea of future terahertz computer tomography imaging and terahertz non-destructive testing research.