Abstract: The key nuclear data for advanced fission energy are important in designing advanced nuclear reactors and facilities for nuclear-waste transmutation. Because the present nuclear data library is limited by experimental condition and energy range, the precision of some nuclear data is low, even some nuclear data are blank. In this paper, the status of the nuclear data and white neutron sources were presented. The back streaming neutron beam at China Spallation Neutron Source (CSNS) has very wide energy spectrum (0.01 eV-200 MeV) and excellent time structure. From the simulation results, it’s obtained that the uncollimated neutron fluence rate is around 9.3×10⁶cm^-2•s^-1 within the given energy range at 80 m away from the target, which accounts for about 53% of the total neutrons. The time resolution of 0.3%-0.9%, which is important for the Time-of-Flight method, can be obtained for both the parasite operation mode with two proton bunches and the dedicated operation mode with a single proton bunch. CSNS white neutron source will be a good facility for nuclear data measurement.