The invention discloses a microwave millimeter wave three-dimensional holographic imaging system signal processing and imaging method. Echo signals are obtained in the microwave millimeter wave antenna array scanning process, and image focusing is carried out on a (y,k) dimension through a phase displacement migration algorithm; image focusing is carried out on the x-dimension by adopting a backward projection reconstruction method; finally, a three-dimensional complex image of an imaging target is obtained. The method integrates the characteristics of a time domain imaging algorithm and a frequency domain imaging algorithm, decoupling and imaging focusing are carried out on a vertical array dimension and a distance dimension through the phase displacement migration algorithm, the backwardprojection reconstruction algorithm is used for imaging focusing of a planar or cylindrical motion scanning dimension, and the advantages that the backward projection reconstruction algorithm is suitable for any antenna scanning rack and capable of facilitating motion compensation are used, so that the method is suitable for a microwave millimeter wave planar scanning imaging system and a microwave millimeter wave cylindrical scanning imaging system, the aim of being applicable to the two kinds of imaging systems though one-time algorithm development can be achieved, clear imaging can be achieved, and the calculation efficiency is higher.