Ionic liquids (ILs) have been applied as an environmentally friendly solvent in the pretreatment of lignocellulosic biomass for more than a decade. The ILs involved pretreatment processes for cellulases mediated saccharification lead to both the breakdown of cellulose crystallinity and the decrease of lignin content, thereby improving the solubility of cellulose and the accessibility of cellulase. However, most cellulases are partially or completely inactivated in the presence of even low amount of ILs. Immobilized cellulases are found to perform improved stability and higher apparent activity in practical application compared with its free counterparts. Enzyme immobilization therefore has become a promising way to relieve the deactivation of cellulase in ILs. Various immobilization carriers and methods have been developed and achieved satisfactory results in improving the stability, activity, and recycling of cellulases in IL pretreatment systems. This review aims to provide detailed introduction of immobilization methods and carrier materials of cellulase, including natural polysaccharides, synthetic polymers, inorganic materials, magnetic materials, and newly developed composite materials, and illustrate key methodologies in improving the performance of cellulase in the presence of ILs. Especially, novel materials and concepts from the recently representative researches are focused and discussed comprehensively, and future trends in immobilization of cellulases in non-natural ILs environments are speculated in the end.