The reasons to cause the variation of the Fu-Long resort area have been investigated in the study. The resort area is the spit extended from the northern coast of the Shung-si River located at the northeast part of Taiwan. Historical coastlines and the bathymetry surveyed in the last 15 years have been used to interpret the cause of the coastline variation. Numerical simulation of the wave and flow field is performed to assist the interpretation. It is found that the spit may be eroded during typhoon season by the flood from Shung-si River and recovered in the next year if the typhoon occurred in monsoon season in which the eroded sediment carried by northward monsoon waves will be merged to the coastline by the following southward northeast season waves. On the contrary, if the typhoon occurred during northeast wind season, the accompanying southward will carry the eroded sediment further south and the spit may not recover in the next year. It is further found that the source of the sediment from the river has been decreased in the last decade and the coastline retreated in responding the source decrease. Man-made fishery port close to the spit also deposited some sediment and may cause the variation of the coastline.