With the development of magnetic confinement fusion (MCF), it has become feasible for fusion energy to solve the future energy crisis. High-energy neutrons are produced during the fusion reaction. Neutron shielding and the tritium breeding ratio in MCF require a neutron source of high precision. In traditional methods, the neutron source is supposed to be isotropic. However, the double-differential cross sections for nuclear fusion given in the ENDF/B-VI database make it possible to calculate the neutron direction distribution in deuterium-tritium (D-T) plasma. In this study, a Maxwellian reactivity rate database is obtained by extracting double-differential cross-section data from the ENDF/B-VI database and then revising it. Monte Carlo and discrete ordinate methods are used to simulate transportation and fusion in D-T plasma and obtain the angular distribution of the neutron generation rate. The results of a preliminary numerical simulation in a simple model tell us that the difference between anisotropy and isotropy can reach an average of 4.6%. A temperature-corrected double-differential cross-section database and a numerical simulation method are developed to calculate the angular distribution of the neutron generation rate.