Neutron generators can produce mono-energy fast neutrons by fusion reactions. The neutrons from the generators have angular energy and flux distribution. In this study, we measure the angular distribution of neutrons about energy and relative flux produced by DT neutron generator in KRISS (Korea Research Institute of Standards and Science) using the diamond detector. The carbon in the diamond undergoes a ${ }^{12} \mathrm{C}(\mathrm{n}, \alpha)^{9} \mathrm{Be}$ reaction with a fast neutron, producing an alpha particle whose energy is same as the incident neutron energy minus the Q value (5.702 MeV). For this reason, the diamond detector can directly measure the incident neutron energy without any difficult algorithm or large space for detection. The angle of the neutrons was set relative to the incident direction of the accelerated deuteron beam. Neutron energy was obtained at different angles by ${ }^{12} \mathrm{C}(\mathrm{n}, \alpha){ }^{9} \mathrm{Be}$ peak centroid. Subsequently, it was revealed that the neutron energy angular distribution follows the single-term cosine function. Furthermore, the variance of the neutron energy is larger with smaller angle of neutrons. Relative neutron flux was determined by ${ }^{12} \mathrm{C}(\mathrm{n}, \alpha)^{9} \mathrm{Be}$ peak area and normalized with the neutron flux at the 0°. Relative neutron flux decreased as the larger angle. With this study, DT neutron generator in KRISS can be calibrated about neutron energy and flux corresponding to the angle.