Spintronic devices, with the integration of magnetic materials and microstructures， have been enabling people to make use of the electron spin and charge properties in many applications. Few works, however, have been carried out in modeling these devices based on magnetic tunnel junction (MTJ) technology. Accordingly, this thesis proposes a novel modeling approach as well as an iterative simulation methodology for MTJs. A more comprehensive electrical tunneling model is established for better interpreting the conductance and current generated by the electron tunneling, and this model can also facilitate the iterative simulation of the micromagnetic dynamics. Given the improved tunneling model and the iterative dynamic simulation, the electric characteristics of an MTJ with an external magnetic field can be conveniently computed. Finally, the magnetic sensor design based on the MTJ technology and the fabrication methods are presented. These works would lay a foundation for the future development of new spintronic devices.