The attosecond X-ray pulse which is produced by the interaction between the laser pulse and the relativistic electrons is studied in this paper. The attosecond X-ray pulse is generated by Thomson backscattering from the relativistic electrons. It also discusses the effect of the plasma parameters on the attosecond X-ray. The wavelength of attosecond X-ray pulse becomes shorter when the frequency of the laser or the velocity of the relativistic electrons increases. We obtained the "water window" X-ray by selecting the appropriate laser and plasma parameters. This paper also discusses the effect of relativistic electrons density and density grad on the translation efficiency.