The influence of photo-detector array on the resolution and wavelength accuracy of the spectrometer is studied in both spatial-domain and frequency-domain. Main parameters of spectrometer, such as the center-distance of the photosensitive elements and width of spectral line etc., have been investigated deeply, and computational simulation is presented. A contradiction between resolution and wavelength accuracy is revealed when the width of one Gauss spectral line is less than five times of the center-distance of the photosensitive elements. The conclusion of one spectral line covering 5 sensing element is predicted.