According to the weak mud intercalation existed in the red-bed slope of Triassic period in southwestern Hubei Province, the authors studied the genesis of the intercalation from the geological sedimentary history and regional tectonic mechanics, and analyzed the changing of mineral and grain size during its formation. By doing indoor test the authors studied the strength characteristics and expansibilities of weak intercalation. After the research the authors made whole understanding of intercalation in this region from genesis to characteristics, and the results from the research can provide theoretical basis and references to the design and engineering construction in the similar area.