The invention provides a HoSrMnNi co-doped bismuth ferrite/Mn-doped zinc ferrite composite film and a preparation method thereof. The composite film comprises a Bi<0.89>Ho<0.08>Sr<0.03>Fe<0.95>Mn<0.03>Zn<0.02>O<3> ferroelectric film and a Zn<1-x>MnFe<2>O<4> magnetic film which are compounded together. The preparation method comprises the following steps: preparing the Zn<1-x>MnFe<2>O<4> magnetic film on a substrate via spin coating; and then preparing a plurality of layers of the Bi<0.89>Ho<0.08>Sr<0.03>Fe<0.95>Mn<0.03>Zn<0.02>O<3> film on the magnetic film via spin coating so as to obtain the composite film. According to the invention, a sol-gel process is employed, a plurality of elements are used for doping so as to regulate and improve the ferroelectric performance of the crystal structure of the ferroelectric film and to improve the breakdown resistance of the film in ferroelectric tests and leakage current tests; meanwhile, ferromagnetic Zn<1-x>MnFe<2>O<4> of a spinel structure is used as a magnetic layer; so the composite film with excellent magnetoelectric coupling performance is obtained.