Open check dams are an efficient means of controlling debris flows within channelized gullies. To estimate the trapping and regulating functions of open check dams, it is important to have accurate predictions of the evolution of their blockade behavior. In this study, a series of specially designed physical modeling tests are performed on open check dams subjected to debris flows. Temporary blocking is observed during the trapping process as the blockade forms and breaks. The influence of opening shape, relative opening, and debris-flow bulk density on the blockade behavior is investigated, and an improved evaluation method based on the blockade criterion is proposed. Analysis allows us to determine the critical blockade conditions for various types of dam and debris flow, and to identify the range over which there is a high probability of temporary blocking. The sediment-trapping effectiveness and reduction in instantaneous discharge are strongly related to the value of the blockade criterion, making this criterion very useful for field practices. The experimental results presented in this paper provide a reference for the design of open check dams.