Abstract: Micron-sized silica gel was chemically modified with 3-methacryloxypropyl trimethoxysilane (MPTMS,KH-570) as coupling agent.Double bonds were introduced onto the surface of silica gel particles,and modified particles MPS-SiO₂ were obtained.The poly methyl acrylic acid (PMMA) was grafted on the surface of particles MPS-SiO₂ with the method of "graft from" ,and grafted particles PMMA/SiO₂ were prepared.The chemical structure of the grafed particle PMMA/SiO₂ was characterized by means of infrared spectroscopy (FTIR) and thermogravimetry (TG),and the morphology of the grafting particle PMMA/SiO₂ was observed.The experimental results show that the graft polymerization of methyl acrylic acid (MAA) onto the surface of silica gel particles can be successfully realized with the method of "graft from" .During the graft polymerization,the grafted polymer layer was a hindrance to the subsequent graft polymerization.When the grafted polymer layer reached to a certain density via overlapping and entwisting,a kinetic barrier was built up.There were several factors affecting the grafting degree of polymer,such as monomer concentration,initiator amount and temperature.The grafting degree of polymer increased with the increase of the monomer concentration,and the grafting degree unchanged when the concentration of monomer was over 3%.When the amount of initiator increased or temperature rose,the grafting degree of polymer firstly increased and then decreased.The preparation conditions for the maximum grafting degree were temperature was 70℃,the concentration of monomer was 3% and the amount of initiator was 0.6%.