Objective To explore the clinical similarities and differences between knee rheumatoid arthritis and osteoarthritis and MRI imaging manifestations. Methods 35 patients with knee rheumatoid arthritis (RA) and 41 patients with osteoarthritis (OA) admitted into the hospital were selected as the research object and all received MRI examination. Results In RA group, the damage rates of lateral tibial femoral lateral malleolus of grade III–IV and tibial plateau of grade III–IV respectively were 94.29% and 100% which were higher than 0% and 0% of the OA group and the difference was statistically significant (P<0.05). The probabilities of lateral tibial femoral lateral malleolus, bone marrow edema of tibial plateau and cystic necrosis in RA group were higher than those in OA group. There was no lateral tibial articular lesion in OA group and the difference was statistically significant (P<0.05), the ratios of grade II-III meniscus injury in inside anterior angle, somatic part and the merocerite of RA group respectively were 97.14%, 94.28% and 97.14% which were higher than 12.19%, 29.27% and 14.64% of OA group. The ratios of grade II-III meniscus injury in lateral anterior angle, somatic part and the merocerite of RA group respectively were 85.71%, 88.57% and 88.57% which were higher than 4.88%, 4.88% and 7.31% of the OA group and the differences were statistically significant (P<0.05). The ratios of hyperplasia and freshy joint capsule synovium in RA group was 94.29% which were higher than 19.51% in OA group and the difference was statistically significant. Conclusion The degree of the lesions of cartilago articularis, subchondral bone and meniscus was more serious than that of OA. MRI imageological examination was of high value in the differential diagnosis of RA and OA.