It is very important for the river management to grasp the hydraulic characteristics of flood flow in compound channels. The propagation speed of flood flow in compound channels has not yet been known, although that in simple cross-section channels was showed by Kleitz-Seddon. This study aims to clarify the propagation mechanism of flood flow and compare propagation speed from laboratory experiments with those of the theoretical expression derived for compound channels. As a result, theoretical formula provides a good expression for propagation speed of compound channels. Furthermore, we explain the effect of change in the channel cross-section on the flood propagation speed in rivers. Finally, we investigate propagation characteristics of various flood flows in the Tone River and Edo River.