Provided is a microsphere including a glass sphere core. The glass sphere core includes a first nuclide, a second nuclide and a diffusion region extending inwardly from an outer surface of the glass sphere core, with the second nuclide distributed in the diffusion region. The first nuclide and the second nuclide become radioactive after being activated by neutrons to produce radiations including β-rays or γ-rays, or simultaneously β-rays and γ-rays. A preparation method of a microsphere is also provided.