The work aims to study all the performances of composite film made by chitosan (CS) and poly (3-hydroxybutyrate-co-3-hydroxyhexanoate) (PHBH). With glacial acetic acid as co-solvent, the CS/PHBH biodegradable composite film was prepared by CS and PHBH in the blend casting method. By means of infrared spectrometer, scanning electron microscopy (SEM) and differential thermal analyzer (DTA), etc., the effect of CS/PHBH with various mass ratios on the mechanical property, structure, thermal stability and biodegradability of the composite film was studied. There were intermolecular hydrogen bonds between chitosan and PHBH, and there was a certain interaction between them; meanwhile, the CS/PHBH composite film showed good thermal stability and biodegradability. When the mass ratio of CS/PHBH was 3∶1, the tensile strength and elongation at break of CS/PHBH biodegradable composite film were better than the composite films with other mass ratios. When the mass ratio of CS and PHBH is 3∶1, the composite film with overall performance can be obtained.