In order to minimize the size of the optical system of Czerny-Turner (CT) spectrometer and prevent interference of incident rays and diffracted rays, a complete selection system of structural parameters is created to satisfy the spectral performance. A variant of the grating equation is proposed, and the constraint conditions are determined to prevent interference of incident rays and diffracted rays. A mathematical model of the optical structure is established and the calculation formulas of structural parameters are determined. On this basis, the determination of the parameters is simplified by programming and all design parameters of the optical structure can be directly obtained once the intended resolution, the wavelength range, the NA value and the minimum distance between components in the system are input into the system. A fast and universal design method of CT spectrometer is realized. A design example with a spectral range of 780～1020 nm, a resolution of 0.4 nm and a volume of 54×56×30 mm3 is given for verification. It can provide reference for other designs.