Abstract: Small-scale flume tests and numerical simulations have been widely applied to investigate submarine debris-flow impact on an undersea pipeline. However, the model-prototype similarity has not yet been guaranteed, which prevents trustable application of model results to prototype scenarios. To this end, the Power-law constitutive relation is used to describe the rheological property of submarine debris flow. The scale ratios between model and prototype for various parameters are derived based on Reynolds criterion. The flume tests published in literatures are used to demonstrate the application of derived scale ratios to model-prototype similarity analyses. The parameters of a model can be converted to those of a prototype with reference to derived scale ratios, and vice versa. In addition, the applicability of derived scale ratios is discussed. It is found that, the derived scale ratios are not applicable to Ng geotechnical centrifuge model tests, but to 1g small-scale flume tests and numerical simulations with relatively high shear strain rate of a submarine debris flow. This study will provide theoretical foundation for reaching model-prototype similarity when studying submarine debris-flow impact on an undersea pipeline in a 1g environment.