In this paper, the finite element parameterized model of 1.2 meter terahertz antenna is established for near-field holographic measurement. The structure of 1.2m antenna, which consists of reflector body and tower base, is developed to a prototype of the 5-m Dome A Terahertz Explorer (DATE5). The reflector is made of carbon fiber-reinforced plastics, and tower base is made of steel. For the evaluation of the antenna performances, the gravity load effects of 1.2m antenna have been analyzed by the model. The numerical analysis results show that reflector surface RMS errors due to gravity load decrease with the increase of elevation angle, and the ranges of values of the surface RMS errors are from 0.14μm, to 0.81μm, which has been met the performance requirements of 1.2m antenna. Moreover, the mode shapes and the eigenfrequencies are also studied. The results suggest that the trends of the dependence of first three orders eigenfrequency upon elevation angles are well agreement with those of DATE5: the eigenfrequencies of the first and second orders of the model also decrease with the increase of elevation angle, while the eigenfrequencies of the third order increase with the increase of elevation angle.