Bombyx mori(B. mori) silk was modified with the nano-$TiO_2$ and chitosan dispersion system by the cross linking reactions of citric acid(CA) and maleic anhydride(MA). The average size of the nano-$TiO_2$ particles in the aqueous dispersion system was 36.7 nm. The scanning electron microscopy(SEM) micrographs showed that the nano-$TiO_2$ particles were spherical and homogeneously dispersed in the dispersion system, and the surface of B. mori silk fiber treated with the nano-$TiO_2$ and chitosan dispersion system was rougher than that of the untreated one. X-ray diffraction(XRD) and Fourier transform infrared(FT-IR) Spectrometry indicated that the crystallinity of the B. mori silk fiber increased after treatment. It was also found that the nano-$TiO_2$ and chitosan contributed to significantly enhance the mechanical properties including breaking strength, breaking elongation, initial modulus, rupture work, and elastic recovery property of the B. mori silk fiber. The wrinkle-resistant performance of the treated B. mori silk fabrics was also greatly improved.