An optical system of a spectrometer based on the double Rowland circle optical structure and its related design methods were proposed. The optical path in the detection wavelength range of 200 nm~500 nm was a conventional Rowland circle optical structure. The optical path in the detection wavelength range of 500 nm~700 nm used the zeroth diffraction order subspectral lines diffracted by a concave grating, which were adjusted by a plane reflector to project the spectral lines into another concave grating, and the double Rowland circle optical structure was realized. According to the design requirements and the mutual constraints among the various parameters of the optical system, the various parameters were designed and calculated. Based on Zemax simulation analysis, the optical parameters were adjusted and the feasibility of the optical system was verified. Aiming at the problem of aberration of the planar signal detector on the Rowland circle, the reflector was used to increase the number of signal detectors, and the aberration was reduced by 4.475 μm compared with that of initial structure. The overall optical structure size of the spectrometer was less than 400 mm 500 mm. Simulation results show that the spectral band range measured by the spectrometer can reach 200 nm~700 nm, and the whole band resolution can reach 0.4 nm.