In Tokamak fusion neutronics, the fusion neutron source description is one of the initial inputs, which affects the neutronics analysis result. Based on the study of fusion neutron source model used in ITER and EU DEMO, a numerical model that uses a set of formulae to describe the L&H-mode plasma D-D/D-T fusion neutron source was addressed. Within the framework of engineering design platform for China Fusion Engineering Test Reactor(CFETR), source card generator(SCG) was developed to solve the numerical model utilizing Monte Carlo method, by which a set of plasma physics parameters were read and the SDEF card for MCNP code was produced. On the basis of neutronics analysis on CFETR with helium cooled pebble bed blanket, neutron wall loading, the tritium breeding ratio and global energy multiplication factor resulting from the SCG-produced SDEF card are of differences at 2.02%, 0.18% and 0.23%, respectively, compared with those resulting from EU DEMO source subroutine in L-mode D-T fusion scenario. This numerical model of Tokamak D-D/D-T fusion neutron source and the SCG can be used in the neutronics calculation of CFETR.