A tomography method includes: a step 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; a step of reforming the 2×N projected energy spectral data at the 2×N individual discrete projection angles and establishing corresponding projection intensity data; and, a step of basing on the projection intensity data and the 2×N projected energy spectral data at the 2×N individual discrete projection angles to calculate the material decomposition images. In addition, a tomography system is also provided.