Electron cyclotron emission imaging system in the frequency range of 95 GHz ～125 GHz is going to be constructed for a two-dimensional diagnosis of the electron temperature profiles and fluctuations on the HT-7 Tokamak. The optical design for the ECEI diagnostic system is completed. Because of the superconducting technology used in HT-7, the vacuum chamber is rather thick (630 mm), the height of the horizontal windows is limited (maximum 450 mm), which constrains greatly the ECE imaging Gaussian beam that passing through the windows. We here comes to make a design compromise between the number of the beams that can pass through the windows and the spatial resolution (around 1.1 cm). We also find that due to the field curvature of the optical system, the gaussian beams of edge channels are always overlapped. To flatten the field curvature, it is needed to insert a concave made of a material with a low refractive index (compared with the one used in the convex). But the suitable material has not been available so far, therefore the deterioration of the resolution in some channels (e.g. the edge channels) is acceptable.