The Quadratic Electro-optic (QEO) coefficient is a very important parameter in the evaluation of the QEO effect of the organic polymer,which could be expressed as a 6×6 tensor.By the utilization of the symmetric characteristic of the tensor,algebra relation between the elements in the tensor and refraction index ellipsoid equation,an approach base on Attenuated-total-reflection (ATR) technology was proposed for the measurement of the QEO coefficient of the organic polymer.In the measurement,elements S₁₁and S₁₂in the tensor could be obtained by choosing TM mode and TE mode respectively as the polarization mode of the incident light beam.Then,S₄₄and DC Kerr Coefficient could be calculated using the known algebra relation equation.Consequently,the value of all elements in the QEO coefficient tensor is obtained.