Formation energy in the carbonate fractured-vuggy reservoir becomes less along with the exploitation. Nitrogen flooding can effectively complement the formation energy，and enhance the capacity of production. Only appropriate injection rate，injection timing and injection mode can achieve the best displacement effect of the nitrogen flooding. A visualized physical simulation model of the fractured-vuggy reservoir was designed based on geological structure data and dynamic production data. Influencing factors on nitrogen injection including injection rate，injection timing and injection mode were analyzed when bottom water energy is not enough in laboratory. The results show that the injection rate has great influence on sweep efficiency and gas channeling and the ultimate recovery efficiency would be low under inappropriate injection rate.Injection timing has influence on water flooding and recovery efficiency. If the opportunity of nitrogen injection is too early，water flooding effects will be poor；and if the opportunity of nitrogen injection is too late，nitrogen flooding effects will be poor. Under the condition of recovery efficiency of 20% by water drive，continuous nitrogen injection can improve the recovery efficiency to 47.09%，while alternating injection of water and nitrogen can improve the recovery efficiency to 60.08%，and alternating injection of surfactant water and nitrogen can improve the recovery efficiency to 61.45%.