The ultra-intense terahertz radiation from laser plasma interaction is widely studied. The terahertz radiation from ultra- intense laser pulse driven wire target is studied by using the radiation theory of antenna proposed by Smith. The expressions of the radiation field are obtained and the space radiation field and frequency spectrum are presented. Based on the study of the influence of the ratio of laser duration to target length on radiation field distribution, the optimum laser duration for a constant target length is discussed, and the modulation of the target length on the radiation field for a constant laser condition is obtained. Theoretical analysis indicates that the range of frequency is determined by the laser duration, and the distribution of spectrum is determined by the ratio of laser duration to target length, which provides theoretical basement for the experiment design.