The invention discloses a modified titanium-silicon molecular sieve, a modification method, and application thereof in propylene epoxidation reaction. The modified titanium-silicon molecular sieve is obtained by the following steps: dissolving barium salt in water to prepare a barium salt aqueous solution, and then adding a strip-shaped titanium-silicon molecular sieve, wherein the weight ratio of the barium salt to the water to the strip-shaped titanium-silicon molecular sieve is (0.001-0.5):(0.1-5):1; and performing impregnation for 1-72h, performing filtration, drying a solid at 80-120 DEG C for 3-5h, and then performing roasting at 500-550 DEG C for 4-12h to obtain the modified titanium-silicon molecular sieve, wherein the strip-shaped titanium-silicon molecular sieve is obtained by mixing titanium-silicon molecular sieve raw powder with sesbania cannabina powder and silica sol uniformly and then performing strip extrusion forming, and the barium salt is barium nitrate, barium acetate or barium chloride. The modified molecular sieve is a strip-shaped titanium-silicon molecular sieve with an MFI structure; and as a catalyst, the modified molecular sieve is applied to a liquid phase propylene epoxidation process. The modification method disclosed by the invention is simple in operation process, and due to a mutual synergistic effect between the barium salt and the titanium-silicon molecular sieve, the modification method, when applied to the propylene epoxidation reaction, can obviously reduce invalid decomposition of hydrogen peroxide as well as effectively improve the effective utilization of hydrogen peroxide and the selectivity of a product namely propylene epoxide.