Coix seed powder was modified by ultra-high pressure, and studied the physicochemical properties after modification. Based on single factor tests, the concentration of Coix Lachryma-jobi flour, pH, pressure, pressure-holding and aging time were optimized by orthogonal test to improve the yield of Coix Lachryma-jobi resistant starch. The optimized conditions were as followed: Coix Lachryma-jobi flour content 20%, pressure 600 MPa, pH 6.0, ageing time 36 h, pressure-holding time 15 min, and the yield was 17.26%. The modified Coix seed powder not only improved 90% yield of resistant starch in Coix Lachryma-jobi, but also improved the freeze-thaw stability, coagulation and solubility in some certain range, and the swelling capacity and light transmittance declined slightly. So ultra-high-pressure is an ideal treatment to manufacture coix seed powder which is suitable for people to lose weight.