In this paper, a Sagnac interferometer with polarization maintaining fiber (PMF) for vector transversal loading measurement has been proposed and experimentally demonstrated. The light propagated in different axes of the PMF has different velocity because of fiber birefringence, which results in phase difference, and thus interferometer pattern is produced. When the birefringence parameters are affected by transversal loading, the phase difference of the light propagating in different axes will change, and as a result of the interferometer pattern of the Sagnac loop shifts. When transversal loading with the opposite direction is applied on the sensing fiber, the interferometer pattern also shifts, but oppositely to longer or shorter wavelength, by monitoring which vector transversal loading measurement can be achieved. The sensing characteristics when transversal loading is applied in different angles have also been studied. The proposed measurement method has a simple structure, and is easy to implement, which shows a good application prospects in the sensing field.