Combined with the flume experiments and 1D unsteady flow numerical model, the paper has investigated the overtopping breach process of the non-viscous embankment. The breach expansion and the variation process of water level above the breach gate have been studied by series of experiments. Considering the difficulty to monitor the discharge through the breach, 1D unsteady flow numerical model has been applied to simulate discharge variation process. It is found that the width of breach gate and water level above the breach gate are the two key factors which influence the discharge through the breach significantly. Discharge variation process through the breach gate is consistent with the flow rule of side weir. The calibrated flow coefficient is from 0.389 to 0.696. The investigation results can provide scientific basis for disaster prevention and evaluation of embankment burst.