Using the transfer matrix method, we investigated the influence of permittivity error on the properties of magneto-optical multi layer isolator with single-defect, and presented a new type of multi layer structure with multi defect. Compared with single-defect structure, the bandwidth of Faraday rotation frequency response of multi defect structure was increased greatly, and the tolerance of permittivity was increased by one order. Furthermore, the multi defect structure has greater tolerance of film thickness and incidence angle.