The present application provides a polymer microsphere and a preparing method thereof. The polymer microsphere includes a core and a shell coating the core; the core includes at least two magnetic particles and a dispersion located between two neighboring magnetic particles; the shell includes a main shell body and a modifying layer, and the modifying layer is located on one side of the main shell body that is away from the magnetic particles; and a material of the dispersion, a material of the main shell body and a material of the modifying layer are the same. The magnetic particles in the polymer microsphere have a good dispersibility, and, when heated, the magnetic attraction force and the magnetic responsiveness of the polymer microsphere can nearly maintain unchanged.