The invention discloses magnetic composite particles and a preparation method and application thereof. The magnetic composite particles are of a core-shell satellite structure, the magnetic composite particles are prepared from silver-shell magnetic beads and gold nanorods, and the surfaces of the silver-shell magnetic beads are combined with the gold nanorods with poly(2-vinylpyridine); the silver-shell magnetic beads are composed of manganese ferrite and silver shells continuously wrapping the manganese ferrite. The preparation method of the magnetic composite particles comprises the steps that 1, the silver-shell magnetic beads are added into a poly(2-vinylpyridine) solution, ultrasonic treatment is conducted, and the poly(2-vinylpyridine) modified silver-shell magnetic beads are obtained; 2, a gold nanorod solution is prepared; 3, the poly(2-vinylpyridine) modified silver-shell magnetic beads and the gold nanorod solution are mixed, an ultrasonic reaction is conducted, the magnetic composite particles are obtained, and the magnetic composite particles can serve as an SERS reinforced substrate for detection application. The magnetic composite particles have the very good magnetic response capability and SERS property, and the preparation method is simple in technology, high in universality and high in applicability.