In the measurement ofinterference fringe using the linear CCD, thinking ofthe separation of CCD, the integral effect of the pixel, and the sampling speciality of the interference fringe (cosine signal), three problems have been discussed seriously——"how to determine the advisable maximum of the spatial frequency ofthe fringe", "the effect on the sampling ofthe integral effect ofthe pixel", and "the effect on the contrast ratio ofthe fringe ofthe phase matching ofthe pixel".