A coherence length tunable solid-state laser based on the spectral dispersion principle is reported. A grating and several right-angle prisms are taken as the coherence length tunable module, which is then put in the laser resonant cavity to replace a mirror. The beam expanding characteristics of prisms and the dispersion characteristics of the grating are used to continually tune the coherence length of the laser. A resonant cavity based on NdYAG is established. An output laser of 1064 nm with power stability less than 0.5% and tunable coherence lengthes from 10 cm to 50 cm are achieved. Both the experimental results and the theoretical analysis show that there is a good linear relationship between the coherence length and the magnification of prism expander.