A novel natural polymer blend, namely, a semi-interpenetrating polymer network (semi-IPN) composed of crosslinked chitosan with glutaraldehyde and silk fibroin was prepared. The FTIR spectra of the semi-IPN manifested that the chitosan and silk fibroin had a strong hydrogen-bond interaction and formed an interpolymer complex. The semi-IPN showed good pH sensitivity and ion sensitivity. According to the different swelling ratios of the semi-TPN in the buffer solution with different pH Values or the AlCl3 aqueous solution with different concentrations, the semi-TPN could swell and shrink while being put alternately into different pH buffer solutions or AlCl3 aqueous with different concentrations. The semi-IPN could also act as an "artificial muscle" because its swelling-shrinking behavior exhibited a fine reversibility.