讨论了用双频光栅方法对包含突变成份的物体产生的变形条纹进行傅里叶变换时，可能会出现频谱混叠问题.推出了低频光栅的频谱f1与高频光栅的频谱f2不相互混叠的条件，分析了探测器非线性会引起同一光栅间频谱发生混叠情况.考虑到通常情况下低频光栅频谱f1与高频光栅频谱f2的混叠起主要作用，因此在该情况下用计算机仿真与实验验证了：当f2<2f1时，f1与f2相互混叠，物体面形难以恢复；当f2>2f1时，f1与f2不相互混叠，物体面形恢复得很好.

The possibility of frequency overlapping was discussed when the Fourier transformation of deformed fringe for discontinuous object that contain mutation was executed by the method of dual-frequency grating.The condition of separation between f1 of low frequency grating and f2 of high frequency grating was deduced,and frequency overlapping of the same grating because of the nonlinearity of detector was analyzed.For the overlapping between f1 and f2 is the chief condition,computer simulation and experiment on the condition prove that f1 and f2 are overlapped when f2<2f1,f1 and f2 are separated when f2>2f1.