The invention relates to a unimodal 87 Rb isotopic atomic filter used for laser frequency stabilization and a method for filtering by adopting the atomic filter. The filter consists of components of an external cavity laser 1, an optical isolator 2, a first semipermeable semi-reflective mirror 3, a second semipermeable semi-reflective mirror 4, a first high reflectivity mirror 5, a natural rubidium cell 6 and the like. According to the unimodal 87 Rb isotopic atomic filter used for laser frequency stabilization and the filter method thereof, by using the Faraday anomalous dispersion effect of isotopic 87 Rb ground state atoms in a magnetic field, a uniform magnetic field is generated through a magnetic field source, such as a permanent magnet, and the laser and atoms are interacted, so the laser polarization direction is changed. The laser transmission polarization direction is limited by two polarizing prisms, the light wave with specific frequency is chosen, and the goal of filtering is achieved. A system is enabled to be in a good working condition through a temperature control system. The unimodal atomic filter has the advantages of simple structure, high filtering performance, work stability, long service life and the transmission rate of being more than 78.0%. The unimodal 87 Rb isotopic atomic filter used for laser frequency stabilization and the filter method thereof have important significance in the experiment with interaction between light and atoms.