波长移相干涉仪可用于大口径光学元件的测试。其移相量需经过标定方可采用定步长移相算法计算相位分布。在长腔长测试条件下，由于激光器的波长调谐驱动源的精度有限，采用定步长移相算法求解相位分布的精度不高。在分析干涉腔长和波面计算误差的基础上，提出了一种自适应相位筛选计算方法。根据电压相位标定曲线采集多组周期干涉图，对干涉图中的光强值进行均匀分布抽样后，对其进行随机移相计算，求取每帧干涉图精确的步进移相量，从中筛选出移相量为π/2的四帧干涉图，利用四步移相计算公式求得精确的相位分布。实验结果表明，在波长移相干涉仪中运用该方法，可以很好地解决长腔长测试条件下的相位计算问题，与未进行筛选的计算结果比较，其测试精度得到了显著提高。

The wavelength tuning interferometer is applied to measure large optical components. In order to obtain the wavefront using the algorithms with certain phase steps, the steps should be calibrated. When it is measured at long interference cavity length, the calculating precision of algorithms with certain steps is low. It is mostly because of the limited resolution of the laser controller. Based on analyzing the relationship between the interference cavity length and the calculating error of the wavefront, an adaptive phase selecting method is presented. Firstly, several periods of interferograms are sampled according to the voltage-phase calibration curve. Then the intensity values of the interferograms are uniformly sampled. By calculating the sampled intensity values with the randomly phase shifting algorithm, the phase steps between every two interferograms are obtained. According to the steps, four interferograms with π/2 step are chosen from those interferograms. At the end, the measured wavefront is obtained by calculating the four interferograms with four-step phase shifting formula. The experimental result shows the validity of the presented method. It can obtain the wavefront when it is measured at long interference cavity length in the wavelength tuning interferometer. And after comparing with the result of no selection method, it is clear to see that the presented method is of high precision.