Dirac Bogoliubov-de Gennes equation and Blonder-Tinkham-Klapwijk formalism are applied to study the conductance and magnetoresistance of a topological insulator ferromagnet/barrier/ferromagnet/superconductor (F1/B/F2/SC) junction with the in-plane magnetization. We find that the induced in-plane magnetization sets a lower critical incident angle for Andreev reflection and causes a very large magnetoresistance. We find also that both the conductance and magnetoresistance are oscillating functions of the gate voltage exerted on the middle ferromagnetic layer and the thickness of this layer.