Multiple Input Multiple Output Synthetic Aperture Radar(MIMO SAR) imaging systems use multiple channels to obtain multi-directional information about humans, which is suitable for human security scenarios. However, in THz MIMO SAR imaging systems, due to the large number of antenna elements, how to balance the accuracy and computational efficiency of the echo signal model becomes a key challenge. A cylindrical synthetic aperture is employed to irradiate the human to obtain the echo signals, and these echo signals are processed by using the Polar Format Algorithm(PFA) to achieve THz 3D human imaging. The computational efficiency and imaging results of two different echo signal models, the Physical Optics(PO) algorithm and the Ray Tracing(RT) method, are compared by simulation for computing a Perfect Electric Conductor(PEC) material-human body. The results show that the PO algorithm using Graphics Processing Unit(GPU) acceleration performs well in terms of computational efficiency and imaging quality, with less than one hour of computation time to compute the entire cylindrical synthetic aperture echo signal, and the imaging results clearly reproduce the shape of the hazardous object. In addition, the PO algorithm also performs well in calculating echo signals that match the actual material of the human body. The effect of directional antennas with different lobe widths on the imaging results is also explored. This provides a more accurate and efficient echo signal model for future validation and optimization of imaging algorithms.