In this paper, a new lattice Boltzmann model for the ion-acoustic solitary waves in plasma is proposed. By using the Chapman–Enskog expansion and the multi-scale time expansion, a series of partial differential equations in different time scales are obtained. By selecting the appropriate moments of the equilibrium distribution functions, the macroscopic equations are recovered. In numerical examples, we simulate the propagation of the ion-acoustic solitary waves. Numerical results show that the lattice Boltzmann method is an effective tool for the study of the ion-acoustic solitary waves in plasma.