beta-glucosidase (BGL), an important component in cellulase complex, plays a crucial role in cellulose hydrolysis. However, its activity in cellulase system of Trichoderma reesei, the conventional cellulase producer, is extremely low. In this study, beta-glucosidase gene (bgl) from Aspergillus niger was cloned and achieved secreted expression in Pichia pastoris. High-level production of BGL (129 IU/mL) was achieved in a 1 m(3) fermenter by using an optimized mixed-feed strategy, in which glycerol/methanol at the ratio of 1:5 and 30 g/L corn steep powder were fed to maintain the methanol concentration of 0.7% (v/v). The obtained BGL was then used to catalyze the synthesis of sophorose, a strong inducer for cellulase production, from glucose via a transglycosylation reaction. When used the resultant glucose-sophorose mixture (GSM) containing 7.08% sophorose as both carbon source and inducer, the cellulase yield produced by Trichoderma reesei was high up to 95.23 IU/mL (filter paper activity), which was 2.1-fold of that achieved by lactose. These results indicated that the BGL is potential for application in the cost-effective and highly efficient production of Trichoderma reesei cellulase.