Dimer　acid　(DA)　was　grafted　onto　lignin　(EHL)　to　form　a　graft　copolymer　DA-g-EHL.　The　selection　of　the　reaction　type　and　the　optimization　of　the　reaction　conditions　for　the　grafting　reaction　were　conducted　through　orthogonal　and　single　factor　experiments.　FT-IR　and　thermal　analysis　were　used　to　characterize　the　graft　product.　It　was　found　that,　compared　with　free　radical　grafting,　DA　can　be　grafted　onto　EHL　more　effectively　by　ester　condensation　with　strongly　acidic　cation　exchange　resin　as　a　catalyst.　Under　optimum　reaction　conditions,　the　increase　of　acid　value　and　the　yield　of　graft　copolymer　can　reach　about　9.3%　and　83%,　respectively.　The　application　of　DA-g-EHL　in　preparing　modified　phenolic　aldehyde　amine　curing　agent　(PAA)　was　studied.　Results　showed　that　the　flexibility　of　the　epoxy　resin　cured　by　DA-g-EHL　modified　PAA　is　significant　higher　than　that　of　the　resin　cured　by　EHL　modified　PAA.　The　graft　of　DA　onto　EHL　may　reduce　the　rigidity　of　EHL　and　the　chain　stiffness　of　the　PAA　modified　by　EHL.