Refractive index (RI) is an important parameter of spectacle lens,which affects the thickness and comfort of spectacle lens.The accurate measurement of RI provides guidance for patients with ametropia to choose appropriate spectacle lens.This paper presents a method for measuring the RI of formed spectacle lens by frequency domain optical coherence tomography (OCT) system.Based on the optical path matching method, the RI can be obtained by the pattern of two interferences before and after placing the spectacle lens,combined with simple data analysis and calculation. This paper also introduces the working principle and device of this method.Firstly,the RI of a K9 concave lens is measured,and the result is 1.507 at 1 310 nm.The relative error is less than 2%,which verifies the rationality and feasibility of this method. Then,the RI of spectacle lens is measured by this method,and its RI is 1.554 at 1 310 nm.The expanded uncertainty of the measurement result is calculated as 0.008 6 (k=2).This method is a non-contact measurement,which will not damage the lens.It also has the advantages of simple operation and low relative error.It can meet the requirements for the accuracy of spectacle lens RI.