Immobilizing cellulase for improving its hydrolysis activity and recyclability is critical for a cost-effective and environment-friendly conversion of cellulosic biomass. However, developing a strategy for achieving a high mass-transfer rate and good separation efficiency between an insoluble cellulose substrate and cellulase remains difficult. Instead of the traditional method, a single-enzyme molecular modification method is used in this study. To modify cellulase and provide it with a temperature-pH dual responsive property, systemized poly(acrylic-acrylonitrile) (PAA-PAN) molecular arms are used. The modified cellulase can reversibly transform between liquid and solid phases. In the liquid phase, the modified cellulase can adjust its active center, increasing its hydrolysis efficiency and separation efficiency. Cellulase and glucose products can be easily separated in the solid phase, allowing the reuse of cellulase. The results show that the modified cellulase's hydrolysis efficiency is comparable to that of free cellulase and that the modified enzyme preserves more than 60% of its initial activity after 15 batches of efficient hydrolysis. Thus, the proposed modification route considerably lowers the cost of cellulose enzymatic hydrolysis.