Abstract: The polychromatic spectrum leads to cup or streak beam hardening artifacts and reduces the image quality in X-CT (X-ray computed tomography). A correction method for beam hardening, involving simple operations of the original polychromatic projection sinogram, was presented based on the analysis of three physics properties implied by beam hardening. Its correction principle was deduced mathematically. A noise reduction method was proposed to suppress the noise enlarged by the harden correction by processing the high-frequency and the low-frequency components in the projection sinogram respectively. The validity of this method was proved by correction results from computer simulations and CT scan experiments of two typical objects. A prior CT scan and complex operations, which were need for the conventional beam hardening correction method with the polynomial fit technique to create the correction models, were not necessary for this correction method. So it is much simpler and quicker, with better signal-noise-ratio, and not affected by scan conditions.