Based on practical experiments, a new method to eliminate beam hardening effect causing cup-like artifacts in CT reconstruction, is demonstrated. The digital X-ray set FAXITRON MX-20 with a high resolution, of which the focal length of the X-ray tube is 20 μm, and the gray scale of the detecting board is 16 bit, is adopted to detect samples with different thickness. Intensities of the X-ray transmitting samples of different thickness are recorded. The exponential fitting method is used to fit the related curves, and by the fitting curves the exponential correction formula is derived. By taking photons of a cylindrical sample by the micro-CT system, we reconstruct a slice of the sample with the fan-beam filtered back-projection algorithm and validate the method. The error of the exponential fitting is less than 1/3 of the results by the conventional two-order polynomial fitting. In the CT reconstruction, the clear cup-like artifact and gray scale ununiformity of the slice before hardening correction are eliminated by the exponential fitting.