This paper uses difference-in-differences model to explore the influence of the establishment of urban agglomeration on regional economic growth on the west coast of the Taiwan Strait. The results show that the establishment of urban agglomeration on the west coast of the Taiwan Strait has a significant positive effect on the growth of the regional economy, and the effectiveness is still significantly positive after many control variables are added. The test based on the PSM-DID also gets basically the same conclusion. Therefore, it is suggested to strengthen the support and guidance of the local government, reinforce the core leading role of the central city in the construction of the urban agglomeration on the west coast of the Taiwan Strait, and implement policies according to the local conditions to promote the industrial division and cooperation in the region, so as to further promote the growth of the regional economy.