With the rapid development of spectral analysis technology in the information age, spectral instrument becomes a preferred access to information in various fields for its performance like high precision, low intrusion and small form factor. With the basic theory of optical design as guidance, echelle grating as key part, high resolution and wide detection wavelength as design target, a small size echelle spectrograph based on Czerny-Turner optical structure is designed. The structure of the system parameters is obtained based on the theoretical computation, and the optical system is simulated by the optical design software Zemax. The design results show that the theoretical resolution of the system, which works in the spectrum range from 200 nm to 800 nm, is better than 0.1 nm.