Applying radio frequency excitation to a longitudinal flow CO laser,a maximum output power of 66 watts and conversion efficiency of 28% have been achieved with the gas flow rate of 13m/s and the effective gain length of 80 cm.Both discharge tube and electrodes are submerged in liquid nitrogen.The experimental result has shown that the LN 2 layer between electrodes and discharge tube does not absorb RF radiation.The dependence of laser output power on input RF power and on laser gas temperature has been obtained.From this work we have got many useful experimental results for the further development of high power RF excited longitudinal flow CO laser.