Abstract: The poly(ε-caprolactone) (PCL) and chitosan (CS) as excellent biodegradable polymers were blended in glacial acetic acid solution, and then the CS/PCL composite membranes were prepared by casting method with different CS:PCL mass ratios of 0:100, 5:95, 10:90, 15:85, 20: 80, 100:0. The micromorphology and structure characteristics were detected by the XRD, FTIR, ¹HNMR, SEM and AFM. The results show that PCL and CS have good compatibility, and strong hydrogen bonds form between molecules and new chemical bonds between PCL end carboxyl and CS side chain hydroxyl, which makes the structure of CS/PCL composite membranes stable. The blend ratio of CS/PCL composite membranes has a great influence on the structure characteristics and micromorphology. The crystallinity and porosity of CS/PCL(10:90)composite membranes are 29.97% and 85.61% respectively, and it shows prevented leakage surface and internal connected porous microstructure. All the results initially identifies 10:90 as the best blend ratio between CS and PCL. The micromorphology and structure analysis of CS/PCL composite membranes with different blend ratios provide an important theoretical basis for their development and application.