Based on the transfer matrix method, we investigate the effects of Rashba spin-orbit interaction and magnetic field on the electron transport in a quasi one-dimensional FM/S/FM system, where FM and S represent the ferromagnetic metal and semiconductor, respectively. The results show that the oscillating scope of the transmission increases with the magnetic field increasing. In the antiferromagnetic alignment, the spin-up and spin-down electrons make the same contribution to the transmission even if a magnetic field is applied. In the ferromagnetic alignment, however, at certain strengths of Rashba spin-orbit interaction and of magnetic field, the transmission coefficient for spin-up electrons is larger than that for spin-down electrons, and the sign of the spin polarization changes, which is opposite to that in the absence of the magnetic field.