Abstract: In the terahertz band, most targets are in the scope of near field. The computation method of the far field RCS is not applicative, therefore, the computational formula of the near-field Radar Cross Section (RCS) is deduced. The occlusion judgment consumes a long time in the Physical Optics (PO) method because of the huge amount of surface elements, and the computational error is unacceptable in the GRaphical-Electromagnetic COmputing (GRECO) method using pixels as the unit of calculation. To deal with the above problem in the PO method and the GRECO method, based on the computational parameters pretreatment, a fast computational method of near field RCS using surface element as the calculating unit and the pixel is used as the occlusion judgment unit is proposed for the complex objects in terahertz band. The method ensures the calculation accuracy, and greatly reduces the computational complexity, and the time consumption of occlusion judging. The calculation of the near-field RCS produced by a square plate, a sphere and a satellite is studied in terahertz band. The results show that this method is efficient and accurate.