Sea-level rise due to global warming and over-exploitation of groundwater resources in coastal areas will induce seawater intrusion into inland groundwater which is leading to the migration of the transition zone, and is affecting the security of regional social economy and water resources. Taking the blue economic zone of Shandong Peninsula as the research background, selecting the coastal area of Longkou and Zhaoyuan as the study area, this paper firstly depicts the groundwater flow field pattern in the research area, and then carries out the quantitative analysis for the migration patterns of the transition zone under changing groundwater levels. The results demonstrate that the width of sea-land transitional zone in the research area is about 1.5–4.5 km. The groundwater level is higher, the migration speed of the sea-land transitional zone is smaller. The results are of significance to study the migration of the sea-land transitional zone in the blue economic zone of Shandong peninsula.