Focal plane assembly (FPA) is an important component for modern remote sensing instruments. Array or linear CCD/CMOS detectors are usually applied. Linear detectors are often used in the space project to have a wider swath. In a remote-sensing project, five spectral ranges are desired. The spectral ranges are designated to be one panchromatic (PAN) band from 450 to 700 nm and four multispectral (MS) bands from 455 to 900 nm. Pixel size of the PAN band is 10 μm, and those for MS are 20 μm. Pixel numbers are 12,000 and 6,000 for PAN and MS bands, respectively. The FPA is consisted of a filter with five stripe band-pass thin films, filter mask and a five-line detector. The arrangement of the detector is B1, B2, Pan, B3 and B4 from the top to the bottom. In order to give the alignment tolerance, an analysis of the parameters of each component in FPA has been performed. Ray tracing method has been applied to have an image projection onto the plane where thin films are located. Spread sheet computation was adopted to simulate the situations when the alignment parameters were changed. According to the analysis, some supplement wideness to the stripe thin films has to be added to have a satisfied alignment tolerance.