We have developed 8Ch array GPR system "Yakumo" and have demonstrated the performance of the multistatic radar. At first, the effect of the antenna polarization and the antenna spacing to GPR signal in the multistatic GPR system was evaluated by a laboratory experiment. Using this multistatic GPR system, we can estimate the vertical profile of the electromagnetic wave velocity by CMP method at every position while operating the system along a survey line. However, in order to improve the quality of the CMP data, antenna polarization should be perpendicular to the direction of the survey line, which is 90 degree rotated from conventional GPR measurements. We found that this arrangement may decrease the quality of B-scan of GPR data. We then rotated the antenna polarization, so that the antenna polarization can be set perpendicular to the direction of survey. The B-scan quality was improved, but CMP data quality was decreased. Meanwhile, we have not observed much difference in C-scan images.