A visualized 2D physical model was designed and fabricated according to similarity theory for researching the subsequent EOR methods after water flooding in fractured-cavity carbonate reservoirs. The remaining oil types and distribution after water flooding were first studied. The mechanisms of activating the remaining oil by N₂ were researched later. Three factors: gas injection rate, gas injection style (continuous gas injection, WAG, gas injection at intervals and pulse gas injection) and gas injection well types influence the EOR effect of N₂. The experimental results showed that the remaining oil after water flooding could be divided into four types including attic oil, corner oil, bypass oil and oil films. The injected N₂ could replace the attic oil as much as possible. Meanwhile, the gas injection rate, gas injection style and gas injection well have much impact on the N₂ EOR effect. An unstable gas injection method was better than continuous gas injection, and WAG is remarkable compared with other gas injection methods. The EOR effect of gas injection from a high positioned well was much better than that of gas injection from a low positioned well when there exists a reasonable gas injection rate. This study could provide a constructive guide for oil field managers to enhance oil recovery with gas drive and also after gas drive. Meanwhile, the shape of caves, the complex fractured-cavity structure and other objective factors were realized to be important points for further study.