A radioactive source and preparing as well as applying methods are disclosed. According to the method of preparing the radioactive source, when a preset dose of a radiopharmaceutical with a half-life shorter than a preset threshold is provided, a solid radioactive source having a predetermined shape may be obtained by mixing and moulding the radiopharmaceutical with a preset solution and a moulding material. The moulding material may comprise a curing agent and/or a water-absorbing material.