Relative hidden degree is of far-reaching importance to the research of incipient motion and transportation of sediment particles. This paper presents an overview on some of the research achievements by the author in the theory and application of sediment relative hidden degree, including the latest researches covering the different dimensionality of relative hidden degree, the regularity of its distribution, incipient velocity of sediment on bed slope and bank slope, demonstration on incipient characteristic of wide grading non  uniform sediment, analysis on Shields fillet curve, and experiment on underwater internal friction angle. Finally, prospect of its experiment research was looked forward.