Trichoderma reesei, a superior cellulase source for industrial applications, is a genus of filamentous fungi with an exceptional potential to produce various enzymes and proteins including cellulases, hemicellulases, and hydrophobins. Growing on easy-access low-cost substrates, as well as a broad range of products produced by T. reesei, represent this genus as the first option for bio-industries to produce required enzymes and proteins with an efficient direction of bioprocess. Recently, many researchers have made efforts to improve the yield of T. reesei cellulases using recombinant strains, optimization of the substrates, and applying the synergistic effects of co-cultivation using different microorganisms. The current findings may help industries such as biofuel producers to reduce the cost of cellulase production by up to 40\%. In this review, recent advances in last five years regarding the improvement in cellulase productivity using T. reesei have been pointed out and the highlights have been summarized.