In this paper, a terahertz (THz) radar security imaging method for multi-target screening is proposed. This imaging system is constituted of several transceivers to get multi-angle echo data. Through aperture synthesis and target detection processing of the multi-angle radar echo data, the multi-target scene can be segmented into several subscenes with each single target inside. In order to fast reconstruct the images of subscenes without the hypothesis of plane wave decomposition, which can cause severe defocus and distortion at the edge of THz radar near-field imaging results, wavenumber domain algorithm is modified for parallel processing of all subscenes data with the center locations of subscenes. Furthermore, convolution integral in slow time is used to speed up the processing of subscenes imaging with fast Fourier transform. Simulation results are analyzed and compared to demonstrate the performance and effectiveness of our method. Moreover, verifiable experiments are designed for proof-of-concept, where imaging scenes are rotating along with a fixed speed turntable. The experimental data are transmitted and received by a stationary THz radar, which operates at 340 GHz with the bandwidth of 28.8 GHz and the output peak power of 5 mW.