A series of semi-interpenetrating polymer network (semi-IPN) films coded as UB from castor oil-based polyurethane (PU) and benzyl konjac glucomannan (B-KGM) we're prepared, and they have good or certain miscibility over entire composition range. Morphology, miscibility and properties of the UB films were investigated by using scanning electron microscopy (SEM), differential scanning calorimetry, dynamic mechanical analysis, ultraviolet spectrometer. wide-angle X-ray diffraction and tensile test. The results indicated that the UB films exhibited good miscibility when B-KGM content was lower than 15 wt%, resulting in relatively high light transmittance, breaking elongation and density. With an increase of the B-KGM content from 20 to 80 wt%, a certain degree of phase separation between PU and B-KGM occurred in the UB films. The tensile strength of the films UB increased from 7 to 45 MPa with an increase of B-KGM content from 0 to 80 wt%. By extracting the B-KGM with N,N-dimethyl form amide from the semi-TPN, the morphology and phase domain size of the UB films were clearly observed by SEM. A continuous phase and dual-continuous phase model describing the semi-IPN were proposed to illustrate the morphology and its transition.