In this study, composite membranes were prepared from mixed solution of polyvinylidene fluoride (PVDF) and cellulose via the non-solvent-induced phase separation (NIPS) method. N, N-dimethylacetamide (DMAc) and 1-butyl-3-methylimidazolium chloride ([Bmim]Cl) were used as the solvent for PVDF and cellulose, respectively. SEM and in situ scanning techniques were used to investigate the morphology of the prepared membranes. The results showed that viscose cellulose/[Bmim]Cl solution acted as a porogenic agent during the membrane preparation process. Hydrophilicity of the composites was evaluated by water contact angle, moisture regain and equilibrium water uptake, which demonstrated that the wettability of the membranes was associated with the hydrophilic group and the roughness of the surface. Most importantly, the alpha -> beta transformation in PVDF matrix was demonstrated from the results of WAXD, FT-IR and DSC. The quantitative analysis indicated that the beta-phase content in PVDF reached 90.1% when cellulose content was 5%, which is higher than many published references and was ascribed to the cooperation of cellulose and ionic liquid. Besides, the crystallinity, thermal stability and mechanical properties of the composite membranes were studied as well.