Diamond is considered a promising detector in radiobiological studies. However, the difference in densities between diamond and tissue imply that their energy deposition spectra are not identical, even for diamond and tissues of the same size. The energy deposition spectrum in diamond was converted to match a tissue sample of the same size. A method based on a mathematical model of energy deposition distribution and the Fourier transform was proposed. The results indicate that the spectra converted from diamond to tissue align closely with those of the tissue. Nevertheless, the applicability of this method is constrained by the mathematical model of energy deposition distribution. Thus, developing a mathematical model that describes the energy deposition spectrum under various conditions can enhance the applicability of this conversion method.