The structure of three kinds of ammoxidative lignosulfonate was studied by elementary analysis、GPC、FTIR　and UV et al.. The proper reaction mechanism based on investigation was provided. Results indicated that:molecular weights of products decreased; aromatic structure degraded partly; nitrogen contents increased and C／N ratio decreased. Among three lignins (CaLs、SEP and CA），the nitrogen content of SFP increased, most N mainly exits in amine、amide and cyclic bonded nitrogen et al.