In this paper, we propose a scheme to generate tunable coherent X-ray radiation for future light source applications. This scheme uses an energy chirped electron beam, a laser modulator, a laser chirper and two bunch compressors to generate a prebunched kilo-Ampere current electron beam from a few tens Ampere electron beam out of a linac. The initial modulation energy wavelength can be compressed by a factor of 1+hbR56a in phase space, where h b is the energy bunch length chirp introduced by the laser chirper, R56a is the momentum compaction factor of the first bunch compressor. As an illustration, we present an example to generate more than 400MW, 170attoseconds pulse, 1nm coherent X-ray radiation using a 60A electron beam out of the linac and 200nm laser seed. Both the final wavelength and the radiation pulse length in the proposed scheme are tunable by adjusting the compression factor and the laser parameters.