The Faraday effect is a kind of phenomenon that may cause the rotation of the optical vector when the linearly polarized light is passing through a magneto-optical medium under the influence of an external magnetic field. The angle of rotation of the polarization direction of the light is linearly proportional to component of the magnetic field along the direction of propagation of the light wave. In this paper，the space magnetic field is measured innovatively with the Faraday magneto-optical effect，it can reduce the measurement error of the goniometer and find the exact position of extinction by using the method of the penumbra. The magnetic induction intensity B = 0. 2876 mT of the magnetic field in the laboratory environment is measured and the magnitude of the magnetic declination is θ = 7.6884°. The relative error of the magnetic induction intensity is ηB = 4.6% and the relative error of the magnetic declination is ηθ = 9.8% compared with the data measured using the magnetoresistive sensor.