Abstract: Twyman-Green interference plays an important role in high-precision optical measurement. Anomalous interference pattern often appears in TwymanGreen Interferometer when CCD is used as an image sensor, which prevents scientific researchers from recording and testing real pattern accurately. Therefore, the principle of optical Moir and the spacing structure of CCD are used to analyze the anomalous interference pattern, which is proven to be Moir pattern theore tically. Based on the optical field distribution calculation, numerical simulation is used to recover the anomalous pattern to further verify the theory. Moir fringe hinders the observation of interference fringes and should be decreased or even eliminated by using a proper CCD or changing the CCD detector sampling algorithm.