This paper presents a three-dimensional finite element method (FEM) model of horizontal Hall sensor in COMSOL Multiphysics. The model aims to simulate the sensor's performance in a straightforward way and provides a means to simulate more complex applications with other physics modules. Compared with traditional two-dimensional models, the three-dimensional model is more flexible in designing Hall sensor and shows great significance in verifying the performance of sensors with different materials and geometries. By changing model parameters and comparing simulation results, an optimal design solution can be achieved effectively and economically. The presented Hall sensor achieves a sensitivity of 0.0669 V/(VT). Basic circuit modules of a complete sensor system are also introduced.