To overcome the problems of the present grating spectrometer, such as low resolution, large aberration, and large size, a kind of Czerny-Turner spectrometer optical system whose effective wavelength range is from 350 nm to 450 nm was designed based on the working princle spectrometers and the aberration theory. Parameters of the optical elements and structure were calculated. The ray tracing, simulation and optimization for the optical system were carried out with optical design Zemax software. The theoretical and experimental results demonstrate that the optical system can operate in 350～450 nm waveband with resolution less than 0.1 nm. The optical system size was 105mm×105 mm×20 mm, it is characterized by simple structure, small size, high spectral resolution, and good stability.