The invention discloses a low-cost safe preservation method for high-purity barium nitrate. Low-cost safe preservation is finally achieved through taking a dense polyurethane film envelope, which is dominated by polyester polyurethane and assisted by polyether polyurethane, as a matrix of an encapsulating material, taking blocked isocyanate as a cross-linker, taking starch grafted sodium acrylateas a blocking agent of unsaturated groups of the dense polyurethane film envelope and meanwhile as a water absorption functional ingredient of the entire encapsulating material, finally obtaining theencapsulating material, and then, subjecting high-purity barium nitrate to vacuum encapsulation by employing the material. The method has the advantages of high density, low cost, high water absorptivity and high reliability.