Abstract: Comprehensive R -matrix analysis of ~(16)O system is done at excitation energies below 10. 5 MeV, involving all experimental data of reactions ~(16)O(n.n )~(16)O, ~(16)O(n,α)~(13)C and ~(13)C(α,α)~(13)C. The final results are very good. Time neutron cross sections from this calculation are used in The Chinese Evaluated Nuclear Data Library (CENDL-2) and the ENDF/B-6 of USA. Some viewes of determining the background, channel radius and boundary conditions are given.