Accurately identifying the boundary of the core areas in the process of urban agglomeration construction is an important part of urban agglomeration research. In this paper, a method of extracting urban agglomeration growth boundary is proposed: using spatial syntax to analyze urban agglomeration road network, fusing the four analysis indicators into a new index "urban agglomeration cluster degree", and putting forward the "urban agglomeration cluster degree" contour and "urban agglomeration cluster degree" curve, finding the best threshold through mathematical calculation, thus extracting the urban agglomeration core area growth boundary. This paper takes the Changsha-Zhuzhou-Xiangtan urban agglomeration as an example. The research results of this method are compared with those of the classical method. After the data quality factor is removed, the growth boundary recognition error of the core areas of urban agglomeration is expected to be controlled within 10%. Experiments show that the urban agglomeration core area growth boundary recognition method based on spatial syntax theory is easy to obtain research data, and has a wide application range and high reliability. The research content and methods proposed in this paper can provide a new idea for urban and urban agglomeration research.