Through laboratory experiments of the evolution of an internal solitary wave (ISW) of depression over step topography in a large stratified fluid tank, the propagating characteristics of the ISW along the mutation topography of the seabed of the South China Sea were studied. The process of the interaction of the ISW and the step topography was shown using layered dye-injection techniques and its structure was quantitatively measured with multi-point combined conductivity-probe arrays. The results show that mutation topography can lead to an amplitude increase of the ISW near the step and cause the waveform to steepen. Further, dynamic phenomena, such as the trail wave train and polarity reversal, are generated.