The magnetic properties of the soft magnetic sensitive film are the key factors to determine the performance of the magnetic sensor. In order to ensure process compatibility, the sensitive film is usually fabricated by magnetron sputtering, and its performance is generally poor, which greatly restricts the development of magnetic sensors. Therefore, how to fabricate thin sensitive film on silicon substrate which meets the performance requirements of magnetic sensor and is compatible with the process of MEMS is an urgent problem to be solved. The correlation research indicated, change of microstructure is conducive to improving the magnetic performances of sensitive film. In this paper, nanoporous thin films were prepared by standard MEMS technology. The related characterization and testing of sensitive films with different apertures were carried out, and the influence of aperture size on the soft magnetic properties of thin films was analyzed. The porous structure with more than 50nm pore size can reduce the Hs and Hc of sensitive film, and the effect of 100nm structures is the most obvious to improve the soft performance of sensitive film. The conclusion of the experimental analysis provides support for the determination of preparation scheme and the performances improvement of sensitive film.