Acoustic self-adaptive focusing in a solid-plate waveguide is theoretically and experimentally studied. The multipath effect exists in the solid plate. A pulse will be widened into a pulsed train and the waveform is distorted. The time-reversal mirrors are applied to study the self-adaptive focusing. The time-reversal effect can be characterized by the focusing gain and the ratio of the principal to the second lobe. It is found theoretically and experimentally that the time-reversal mirrors can compensate automatically for the waveform distortion caused by the multi-path effect.