As an advanced technique capable of finely regulating the properties of materials, the controllable grafting technique has gradually become a research hotspot in the field of material science and technology due to its high flexibility and customization. In this study, the regenerated cellulose membrane was surface grafted with poly glycidyl methacrylate (PGMA) via controllable grafting technique by taking 2-bromoisobutyryl bromide (BIBBr) as initiator and CuBr as catalyst. The effect of several key parameters on the grafting effect were systematically investigated, including dosages of initiator BIBBr, monomer GMA and catalyst, CuBr as well as the reaction temperature. The aim is to introduce epoxy groups in a controllable manner and pave the way for downstream separation and purification. The results show that the amount of initiator BIBBr is directly related to the density of the surface grafted initiator, which can effectively control the grafting rate of GMA. By the optimized conditions, i.e., the dose of initiator BIBBr, which is 3 times of the hydroxyl equivalent, the dose of GMA 17.83 mmol, and of CuBr 0.18 mmol, while the reaction at 60 °C, the grafting reaction may result in a grafting rate up to 10.51% (mass fraction) with an epoxy value 12.63 μmol/g. This study provides an important reference for the functional design of cellulose membranes.