双光束干涉仪的相位调制解调通常会用到椭圆拟合的方法来计算相应的解调参数，提出了一种用于评价这类参数的计算精度的方法。根据自适应的蒙特卡罗法，计算不同噪声水平下椭圆拟合估算的参数的最大偏差；根据实验测得的干涉信号噪声本底的大小，判断拟合的参数的精度。以基于3×3 耦合器的光纤水听器的两路输出方案为例，该方案为提高水听器的解调性能，需研究参数的数值随器件性能的变化规律，因此首先要判定实验中通过椭圆拟合所求得的参数的准确性。将该精度评定方法运用在水听器测量实验中，测量的干涉信号在20 Hz~4 kHz处的噪声本底接近-70 dB·V²/Hz，根据自适应的蒙特卡罗法，得到参数的偏差不超过0.06%和0.08°。

The phase modulation and demodulation of double beam interferometer often use ellipse fitting to calculate relevant parameters, and a method is developed to assess calculation precisions of these parameters. The maximum deviations of parameters calculated by ellipse fitting should be computed in different levels of noise according to adaptive Monte Carlo method; then the precisions of fitted parameters can be estimated according to the noise floor of interference signal which is measured in experiments. The algorithm of fiber-optic hydrophone based on 3×3 coupler using two interference signals is analyzed as an example, and the relationship between the parameter value and device properties needs to be studied in order to improve the demodulation effect of hydrophone. As a result, the precisions of parameters calculated by ellipse fitting in experiments should be assessed firstly. The assessment method of precisions is applied to hydrophone experiments, and the noise floor of measured interference signal is close to -70 dB·V²/Hz from 20 Hz to 4 kHz. The deviations of parameters are less than 0.06% and 0.08° according to adaptive Monte Carlo method.