Space combining beam of Terahertz was designed in the paper. The optical intensity of single THz beam, double THz beams (2×1) and four THz beams (2×2) were calculated in the condition of spatially combining images. Through the obtained images, the relationship between the receiving distance, the Gaussian beam peak separation distance and combining intensity were obtained, and the effect of phase difference on combining beam was analyzed. The results show that THz peak intensity is enhanced by near four and sixteen multiples in the conditions of 2×1 and 2×2 arrangements. The optimal THz beam receiving distances of 2×1 and 2×2 arrangements are found through calculation and images, and they are 0.325 m and 0.223 m. Gaussian beam peak separation distance and peak intensity are nonlinearly inverse relationship, which has no maximum or minimum points. The image of 2×1 arrangement was achieved when there is phase difference between two THz beams, and the minimum point of THz intensity of π was attained in the image. So it can be concluded that the phase difference can be decreased but it can not be avoided.