The Czerny-Turner layout, which is most frequently used in miniature spectrometers, should follow Shafer’s coma-free condition and Fastie’s flat-field principal to eliminate the central wave’s primary coma and maximize its resolution. However, the design process does not take the comas and resolutions at non-central waves into consideration. Based on the theory of primary coma in reflection optical system, the present paper points out that in the crossed beam design, the resolutions at wide spectral region present a “V” shape, while in the M design, the resolutions change little over the whole region, and present an approximately straight line shape, so the latter kind of spectrometer maintains a far more consistent resolution than the former one. Accordingly, this paper designs two kinds of spectrometers with spectrum regions from 400 to 600 nm, and carries out theoretical simulation and contrast experiment. The result demonstrates that for the two designs the resolutions at the fringe wavelength are 3.8 times and 1.5 times respectively that at the central wavelength, which accords with the conclusion of the theoretical simulation.