The high precision detection of GPR (Ground Penetrating Radar) is needed in Engineering and environment geophysics such as landmine detection and engineering inspection. The impulse GPR has some problems of transmitting narrow and high power pulse, while the SFGPR (Step Frequency GPR) has the potential to overcome the problems. We discussed the advantages and disadvantages of SFGPR based on Network analyzer in this paper. In order to building the Ultra-wide band GPR system, the wide-band antenna is needed. We analyzed the ultra-wide band antenna in theory and introduce the principle of ultra-wide band antenna designing. The ultra-wide band antenna was fabricated based on the theory analysis and experiment study. Then the system response of SFGPR system based on Network Analyzer was tested. The test results show that the Vivaldi antenna, which has a smallest opening at the antenna end, has a better performance than the other Vivaldi antennas with regard to received signal magnitude. The system response shows the SFGPR system has the potential to detect the objection with the resolution of less than 1cm.