In order to study the microscopic process in rubrene-doped organic light emitting diodes, two kinds of devices were fabricated by utilizing the host materials of 4,4’-N,N’-dicarbazolebiphenyl (CBP) and tris-8-hydroxyquinoline aluminum (Alq3), as well as the fluorescent dopant material 5,6,11,12-tetraphenylnaphthacene (rubrene). The magneto-electroluminescence (MEL) curves were measured in the temperature range of 20 K to 300 K. It was found that the MEL curves of rubrene dopant with Alq3 and CBP devices were composed of two parts, namely, the low field effect dominated by the intersystem crossing (ISC) process and the high field effect dominated by the triplet-triplet annihilation (TTA) process. Compared with the conventional un-doped device, the low field effects of these three devices exhibit the same change trend at the same temperature. At different temperatures, these devices show diametrically opposite changes. Specifically, the low field effect in un-doped device shows that the ISC process weakens with the decrease of the temperature, but the low field effects of rubrene dopant with Alq3 and CBP devices show that the ISC process increases with decreasing temperature. By analyzing the energy level structure of the device, the emission spectra of host materials and absorption spectra of guest material, it demonstrated that both the carrier trap effect and the Forster energy transfer process were included in the microscopic processes of rubrene dopant with Alq3 and CBP devices. The carrier trap effect mainly affects the high field effect of MEL and is basically independent of temperature changes. This anomalous temperature-dependent behavior of ISC process can be ascribed to the suppression of Forster energy transfer process at low temperatures, leading to an increase in the number of polaron pairs in the host material. Therefore, the ISC interaction between the polaron pairs will increase with decreasing temperature. Our work has a certain role in promoting the understanding for the evolution of microscopic mechanisms in rubrene doped devices.