Oxygen plasma processis usually implemented for selective etching of organic films. The oxygen plasma etches the organic materials non-uniformly, the deep etching generatesthe rough surface morphology. However, high-pressure plasma environment can maintain the initial surface status independent of etching depth. Here, a high-pressureplasma etching method that can reduce the surface roughness of ferroelectric polymer film is presented. After an amorphous polymer having the same etching rate is formed, the surface of the amorphous polymer film is treated with a plasma, which makes it possible to have a smoother surface than the original film. This process is expected to be useful for the surface treatment of all crystalline polymers, including ferroelectric polymers.