The poly(L-lactic acid) (PLLA)/ZnO composite membrane with cluster assemblies microstructure was constructed by a combination of non-solvent induced phase separation (NIPS) and the Breath-Figure method. In this novel method, the controllable diffusion rate between solvent and non-solvent was introduced to the system by adjusting the non-solvent solubility parameters. The humidity was adjusted to control non-solvent solubility parameters in the Breath-Figure method, which avoids the instantaneous phase separation induced by direct coagulation of water droplets. Hydrophobic modified ZnO nanoparticles were used as heterogeneous nucleation points to induce PLLA crystallization and formation of micro-nano structures. Controlling molecular chain growth with crystal nuclei as templates and constructing cluster assemblies microscopic morphology at 99% humidity, and the size of the cluster decreases gradually from 10 μm to 3 μm as the nanoparticles content increased up to 5 wt%. The surface water contact angle could reach 153.8? with cluster morphology. In addition, the porous structure formed by the polymer-lean phase could increase the porosity to 93.1 % and exhibit an excellent oil absorption capacity up to 12.64 g/g. It is foreseeable that porous PLLA/ZnO composite membranes have potential applications as biodegradable oil-water separation materials.