A closed water-dispersible isocyanate modified acrylate copolymer was gradually synthesized by solution polymerization. The polymer is based on amphiphilic properties acrylate long chain, which was synthesized from methoxypolyethylene glycol acrylate (MPEG350A), butyl acrylate (BA), hydroxypropyl acrylate (HPA). Subsequently, condensed with isophorone diisocyanate (IPDI) and finally blocked with methyl ethyl ketoxime (MEKO). Then, a composite sizing agent (PMP) was prepared with 1% wt PAIM and 4% wt polyvinyl alcohol (PVA), which was used for sizing kapok mixed paper. The structure of PAIM was characterized by FTIR and GPC, the effects of the ratio of hydrophilic and hydrophobic monomers and the amount of HPA monomer on the particle size and stability of PAIM dispersion were discussed using DLS and TSI. The effects of isocyanate content on the physical properties of paper were studied, and the application performance was compared with the commercial sizing agent. The results showed that when n(MPEG350A):n(BA)=2:1, w(HPA)=10.1%, w(—NCO)=17.3%, the sizing concentration was 10 %, the paper had a folding endurance of 569 time, a tensile index of 66.83 N·m/g, a tear index of 11.54 mN·m2/g, a stiffness of 92.16 mN, and a contact angle of 80.3°. Compared with the commercially available sizing agent, PMP-3 had a longer storage period. After PMP-3 sizing, paper folding resistance, tensile strength, tearing degree and stiffness were increased by 29.3% ，32.3% , 22.1% ，19.5%, PMP had excellent business application prospects.