[Background] The bioconversion of cellulose has become a research hotspot in the energy, food and chemical industries. However, there are few reports on the cold-adapted fungi with the ability to degrade cellulose. [Objective] To isolate and screen the cold-adapted fungi with high efficiency of cellulose degradation from the rhizosphere soil in the high altitude area of Tibet, and optimize their enzyme production conditions, so as to lay a foundation for their industrial application. [Methods] Cellulolytic strains were screened by the dilution plate coating method, the qualitative analysis of Congo red and the quantitative analysis of enzyme activity. Strains were identified by morphology and ITS rDNA sequence analysis. The fermentation condition was optimized by single factor and response surface methodology. [Results] A cold-adapted fungus, namely NLS-2, was obtained and identified as Penicillium sp. At 15 °C, the optimized culture conditions of strain NLS-2 for producing cellulase were straw powder 2.5%, yeast powder 0.5%, KH2PO4 0.5%, fermentation time 7 d, pH 6.5, shaker speed 170 r/min. [Conclusion] Penicillium sp. NLS-2 can grow at low temperature and efficiently produce cellulose, which has a good application prospect.