Abstract: The acceleration of the industrialization process continuously drives the deepening of the spatial agglomeration of China's manufacturing industry, and has a profound impact on the foreign trade pattern of China's manufacturing industry. Based on the perspective of “scale effect” and “crowding effect”, this paper uses the panel data of 30 provinces from 2003 to 2016 to analyze and verify the influence effect, influence direction, industry and regional heterogeneity of spatial agglomeration on manufacturing export. The results show that: (1) The impact of spatial agglomeration on manufacturing export depends on the trade-off between “scale effect” and “crowding effect”, and there is a significant “inverted U” relationship between them. (2) The deepening of spatial agglomeration can not only expand the export scale, but also optimize the export structure of manufacturing industry to a certain extent. (3) The “crowding effect” of spatial agglomeration on manufacturing export has begun to appear, and the “crowding effect” is the most obvious in the eastern region.