In order to solve the problems of the existing spectrum detection module in Laser-Induced Breakdown Spectroscopy (LIBS) system, such as low resolution and large size, based on the optical design theory, a small size, and high resolution crossed Czerny-Turner spectrometer was designed. Parameters of the structure and optical elements were calculated. The performance analysis and evaluation of the optical system were carried out by using optical design Zemax software. The results show that the optical system whose effective wavelength range is from 340 nm to 440 nm with resolution better than 0.1 nm, and its size was 200 mm×180 mm×60 mm. In addition, in order to verify performance of the spectrometer, the heavy metal solution was detected with the LIBS system. The experimental results demonstrate that it has various advantages, such as high spectral resolution, small size, low cost, simple structure, and good stability.