Based on the theory of electrical spin injection into semiconductors, by conside ring the car riers of spin polarons and spinless bipolarons in organic polymers, we suggested a model of spin injection into organic polymers. It was found that a high curre nt polarization can be obtained by adjusting the spin current polarization in the ferromagnetic layer or the conductivities of the ferromagnetic and organic layers. Effect of the proportion of polarons to carriers on the spin current polarization was discussed.