电光系数是铌酸锂晶体的重要性能参数，密切关系着电光器件的设计和应用. 然而由于铌酸锂晶体的合成条件不相同使得晶体的电光系数没有理论值，给电光系数测量值的误差分析带来困难. 本文从数值分析的角度，利用开源的Python程序包拟合实验数据，得到拟合参数及其不确定度，再由误差传递理论推导出晶体的电光系数及其误差. 本文利用半波电压法测量晶体电光系数的相对误差小于2%，具有很高的精度. 文中还给出了当前广泛使用的Python程序的拟合源代码，欢迎相关科研人员参考使用.

The electro-optical coefficient is an important parameter of lithium niobate crystal, which is closely related to the design and application of electro-optical devices. However, the synthesis conditions of lithium niobate crystals are different and this results in different electro-optical coefficients of each crystal, which brings difficulties to the error analysis of electro-optical coefficients. From the perspective of numerical analysis, Python, the open source package is used to fit the measured data. The specific value of fitting parameters and their uncertainties are obtained, and then the electro-optical coefficient of crystal is derived from the error transfer theory. Numerical analysis shows that the half-wave voltage method has high accuracy in measuring electro-optic coefficient, and its relative error is less than 2%. The fitting code of the widely used program Python is also given in this paper, and relevant researchers are welcome to use for reference.