Ir (PPY)3 and DCJTB doped PVK films were fabricated in the presence of electric field which induced the orientation of polymer molecules, and their photoluminescence and electroluminescence were measured. The influence of electric field-induced orientation on the formation cross-sections of singlet and triplet excitons is investigated. The results showed that the electric field-induced orientation of polymer does not cause significant change in PL spectrum. However, the orientation of polymer results in obvious change in EL spectrum. For the devices based on polarized PVK, the EL from triplet states is reduced, which shows that polarization of PVK leads to the increase in the formation cross-section of singlet exciton and the decrease in the formation of triplet exciton.