The seakeeping of the floatover barge in waves is extremely significant to the design of installation and transportation. The T-shaped barge is a new concept with some unique characteristics dissimilar from conventional barges. In this paper, numerical analyses in frequency domain and time domain were carried out for transportation configuration. The frequency domain analysis used 3D potential flow code WAMIT, and obtained motion response amplitude depending on frequency and other hydrodynamic parameters. In addition, the time domain analysis was also performed using self-made program with FORTRAN code. Based on the convolution theory, a 6-dof time domain equation of motion was built and solved by 4-order Runge-Kutta method, and instantaneous hydrostatic restoring force was calculated to take large amplitude roll motion into consideration. Corresponding model tests were also carried out in the ocean basin of Shanghai Jiao Tong University. Comparison between numerical and experimental results shows that the response amplitude operators agree quite well and the effect of viscous roll damping is obvious. The time domain analysis program was validated by experiment comparing statistic and time series. Furthermore, sensitivity analysis on wave parameters was also executed to find the worst condition.