An ICRF antenna for 6 MW RF power coupling to plasmas has been developed. For long pulse (300 s) and high power operation, the antenna has many cooling channels inside the current strap, Faraday shield, cavity wall and vacuum transmission line to remove the dissipated RF power and incoming plasma heat loads. The RF power test has been performed to ascertain the voltage and current limits of the antenna at the frequency of 30 MHz. During the RF pulse, the peak voltage, forward/reflected powers, temperature on the cavity wall, and gas pressure are measured. Results show the peak voltage of 33.2 kVp for 60 s and 25.2 kVp for 300 s (without cooling).