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The building of check-dams is one of the most effective measures for the conservation of soil and water in the Loess Plateau of China, and the hydro-sedimentologic balance is the most important factor influencing the relative stability of the check-dam systems. This means that the soil and water in small watersheds controlled by the check-dams will be absorbed internally, without the need for raising the height of the dams, if some given parameters have reached certain values. A runoff simulation experiment for a single check-dam and a rainfall simulation experiment for the whole check-dam system has been conducted, and the runoff/rainfall intensity and the parameter RV were determined through the annual erosion rate of the prototype watershed. The results indicated that the raising of the dam-land altitude became slower, and the mean gradient of the gully was kept at a constant. The main reasons causing the check-dam to show a good relative stability are the enlarging of the dam-land area, the alleviating of erosion by the check-dam, and the auto-stabilizing mechanism of the gullies. This study presents a kind of scale-down model experiment in which the ratio of the model geomorphological variable to the corresponding prototype variable keeps constant after the determinate runs of rainfalls, so that the soil and water erosion processes of the prototype could be monitored from the results of the model experiment. Four measures have been suggested for ensuring this ratio is a constant: (1) A bare-land model with an appropriate erosion rate should be used in the experiment. (2) Dimensions of the landform, including the check-dam, should normally be scaled down according to the prototype watershed. (3) Soil similar to those of the prototype should be used. (4) The antecedent water content before each rainfall simulation should be kept constant. [ABSTRACT FROM AUTHOR]