In order to meet the demand for fast steering mirrors (FSM) with 15 mm aperture in constrained space, an in-depth study of magneto-resistive electromagnetically driven FSM was conducted. Theoretical analysis and modelling simulations of magneto-resistive electromagnetic actuators have been carried out. The influence of parameters such as coil, permanent magnet parameters, magnet conductor, air gap and core on driving torque in electromagnetic drives was analyzed. According to the simulation optimization results, a FSM prototype was designed and experimentally tested. The results show that the external dimension of the FSM is Ø24.0 mm×33.5 mm, the angular stroke is 2-D ±1°, the working bandwidth is more than 350 Hz, the weight of the main body is 79 g, calibre 15.0 mm and the average power consumption is 7.36 W. The FSM prototype is small, lightweight, and has a large cornering range, which allows it to be applied to beam pointing in constrained spaces. The procedure disclosed is helpful for small magneto-resistive FSM for applications in space, load weight constraints are high for applications.