By the use of typhoon annual report, best track of JMA, T213 analysis field, satellite image and aerological observation data, the cause of maintenance of Typhoon Rananim (0414) on land is analyzed from diagnostic analyses of synoptic and dynamic conditions. The results show that the water vapour transportation at low layer and the eastern jet and solenoid field generated by the interaction between middle-latitude synoptic system and Rananim are two main reasons of its maintenance on land. Meanwhile its location being under the outflow at the southeast or south direction of intensive divergent field at high layer as well as at low vertical shear regions during its maintenance on land are also two important conditions.