ing at the problems of complex structures and difficult debugging in the current design based on prism-grating combination, we established a mathematical model of dispersion based on prism-grating combination and proposed an optimization method of only changing the relative positions of the prism and grating to increase the spectral dispersion linearity. As a result, we obtained the parameters of the prism-grating combination structure with good linearity. Furthermore, we used optical standard elements to simulate and experimentally verify the correctness of the model, and the results showed that our system had the advantages of 15 cm length, good spectral linearity, and simple structure in the band of 400-1000 nm. Finally, the experiments demonstrated that the overall resolution was better than 2 nm in the band of 420-780 nm, which further proved the effectiveness of the proposed method. In a word, this paper provides a flexible and simple structural design method based on prism-grating combination.