A tomography method, comprising the steps of: having a photon counting detector to undergo a relative motion with respect to an X-Ray source, and capturing 2×N projected energy spectral data at 2×N individual discrete projection angles that divide the relative motion, the N being a positive integer; reforming the 2×N projected energy spectral data at the 2×N individual discrete projection angles, and establishing corresponding projection intensity data; and basing on the projection intensity data and the 2xN projected energy spectral data at the 2×N individual discrete projection angles to calculate material decomposition images wherein the step of "reforming the 2×N projected energy spectral data at the 2×N individual discrete projection angles" includes a step of defining a low-energy threshold and a high-energy threshold larger than the low-energy threshold, each of the 2×N projected energy spectral data at the 2×N individual discrete projection angles being divided by the high-energy threshold and the low-energy threshold so as to produce correspondingly a high-energy spectral data and a low-energy spectral data, a mean energy of the high-energy spectral data being larger than that of the low-energy spectral data, wherein the step of "establishing corresponding projection intensity value" includes the steps of: forming 2×N full-energy projected energy spectral data at the 2×N individual discrete projection angles by combining the individual high-energy spectral data of the 2×N projected energy spectral data at the 2×N individual discrete projection angles with the corresponding low-energy spectral data; integrating the 2×N full-energy projected energy spectral data individually at the 2×N individual discrete projection angles so as to obtain corresponding intensity data at the 2×N discrete projection angles; and combining the intensity data at the 2×N discrete projection angles so as to form the projection intensity data. having a photon counting detector to undergo a relative motion with respect to an X-Ray source, and capturing 2×N projected energy spectral data at 2×N individual discrete projection angles that divide the relative motion, the N being a positive integer; reforming the 2×N projected energy spectral data at the 2×N individual discrete projection angles, and establishing corresponding projection intensity data; and basing on the projection intensity data and the 2xN projected energy spectral data at the 2×N individual discrete projection angles to calculate material decomposition images wherein the step of "reforming the 2×N projected energy spectral data at the 2×N individual discrete projection angles" includes a step of defining a low-energy threshold and a high-energy threshold larger than the low-energy threshold, each of the 2×N projected energy spectral data at the 2×N individual discrete projection angles being divided by the high-energy threshold and the low-energy threshold so as to produce correspondingly a high-energy spectral data and a low-energy spectral data, a mean energy of the high-energy spectral data being larger than that of the low-energy spectral data, wherein the step of "establishing corresponding projection intensity value" includes the steps of: forming 2×N full-energy projected energy spectral data at the 2×N individual discrete projection angles by combining the individual high-energy spectral data of the 2×N projected energy spectral data at the 2×N individual discrete projection angles with the corresponding low-energy spectral data; integrating the 2×N full-energy projected energy spectral data individually at the 2×N individual discrete projection angles so as to obtain corresponding intensity data at the 2×N discrete projection angles; and combining the intensity data at the 2×N discrete projection angles so as to form the projection intensity data. forming 2×N full-energy projected energy spectral data at the 2×N individual discrete projection angles by combining the individual high-energy spectral data of the 2×N projected energy spectral data at the 2×N individual discrete projection angles with the corresponding low-energy spectral data; integrating the 2×N full-energy projected energy spectral data individually at the 2×N individual discrete projection angles so as to obtain corresponding intensity data at the 2×N discrete projection angles; and combining the intensity data at the 2×N discrete projection angles so as to form the projection intensity data.