With the improvement of fabrication technology of optical fiber preform

the fabrication efficiency and preform size have been greatly improved. However

the corresponding testing equipment cannot keep up with the market

and there is no equipment that can complete the geometric parameters measurement of large-size optical fiber preform

especially the concentric parameters of core and clad. Based on the demand of technological breakthrough

this paper analyzes and establishes the theoretical model of optical imaging method to measure the concentricity of core and sheath from the physical characteristics of optical fiber preform

and puts forward the construction scheme of measurement system. The feasibility of the method is verified by experiments and compared with the final product optical fiber results.