Driving liquid crystal photorefractive devices with an alternating electric field instead of the dc electric field can overcome some disadvantages induced by the use of the dc electric field,such as the dynamic scattering,permanent grating,and electrolyte. The formation and the application of coherent amplification of gratings recorded in C60-doped nematic liquid crystal under nonbiased sinusoidal alternative electric field were investigated by using two-beam-coupling experiment. Stable asymmetric energy transfer between two writing beams was observed in this kind of cell,indicating the photorefractive nature of the grating recording in nematic sample under the ac electric field. Large beam-coupling ratio was obtained,and the value was compared with that at a dc electric field. Finally the coherent amplification was realized,and the gain coefficient as high as 190 cm-1 was achieved.