In a stratified fluid tank, experiments on the propagating, shoaling and breaking of the internal solitary waves over a gentle slope similar to the topography in the northeast of the South China Sea are conducted. The qualitative analysis on the evolving characteristics of the internal solitary waves is accomplished by use of the dye-tracing technique, and their quantitative measurement is carried out by using the multi-channel conductivity-probe arrays. It is shown that due to the shoaling effect the internal solitary waves with large amplitude are restrained, but the waves with small amplitude are magnified. The shoaling effect will also lead to the decrease of the propagation velocity of the internal solitary waves. Further, the shoaling effect will bring about strong shear flow instability, and then makes the internal solitary wave broken. The breaking wave will result in the fission from one large amplitude wave into several small amplitude waves with the same polarity. By means of the Mile's stability theory, the instable happening-location of the internal solitary wave over the gentle slope can be described through the Richardson number. The experimental results accord well with the theoretical analyses.