Abstract: In previous experiments on the local scour and protective structures around the navigable waterway regulation structures, several simple simulation methods were utilized for dikes, flexible mattress and frame structures. The influences of these methods on experiment results are not available, and there are not any relevant technical requirements on structure model experiments in the test regulations. In this paper, on the basis of similarity theory, similarity conditions and design methods are proposed for the studies of local scour and protective structures around the navigable waterway regulation structures; based on the composites with characteristics of adjustable density and easy forming, the simulation technology of small scale protective structures is developed; and the influences of joint pattern and geometric similarity deviation on the simulation of the flexible mattresses are studied through flume experiments. The analysis results mentioned above show that the small scale flexible mattress and frame structures should be simulated by a kind of composites having adjustable density and variable formation. Simplifying a tied concrete interlocking block of the D type fiexible mattress as a glued concrete interlocking block has no influences on stability and variation characteristics of the mattress, and the glued concrete interlocking flexible mattress has no influences on the mattress, only having a slight influence on the initial deformation similarity and no great influence on the late. Keeping mass similarity and neglecting geometric similanity of the interlocking block will influence critical instability induced bottom velocities and instable modes of the mattress. The research results could provide a technical reference for the simulation of the local scour and protective structures, and for the modification of the relevant test regulations and codes.