  We investigate electron transporting through a two-dimensional
ferromagnetic/normal/ferromagnetic tunnel junction on the surface of a
three-dimensional topological insulator with taking into $\delta$ doping
account. It is found that the conductance oscillates with the Fermi energy, the
position and the aptitude of the $\delta$ doping. Also the conductance depends
sensitively on the direction of the magnetization of the two ferromagnets,
which originate from the control of the spin flow due to spin-momentum locked.
It is found that the conductance is the maximum at the parallel configuration
while it is minimum at the antiparallel configuration and vice versa, which may
stem from the half wave loss due to the electron wave entering through the
antiparallel configuration. These characters are very helpful for making new
types of magnetoresistance devices due to the practical applications.
