In order to increase core rod size and maintain the ideal deposition efficiency and qualified optical parameters, this paper studies the main factors affecting the core rod size by vapor phase axial deposition method. The number of deposition blowtorch, the flow rate of SiCl4 and the lifting rate of soot body are optimized. In the deposition process of three blowtorches, when the flow rate of SiCl4 in the first and second clad blowtorch is increased to 4.0 slm and 5.0 slm, and the lifting rate is reduced to 85 mm/h, the experimental results show that the deposition rate increases to 15.8 g/min, the bulk density of soot body increases to 0.319 g/cm3, the core rod size increases to 99.1 mm, and the deposition efficiency reaches 52.2%, and the refractive index profile of G.652D single-mode fiber is maintained.