We investigate the interaction between acoustic and optical signals in Bragg gratings. Using the multiple-scale method, we convert the optoacoustic coupled mode equations into a standard nonlinear Schrdinger equation. Thus, we obtain approximate solutions of the optoacoustic coupled mode equations, such as the single-soliton solutions and multiple-soliton solutions. Furthermore, we discuss the properties of slowing light of optoacoustic solitons and the interaction of two-soliton solutions.