The slope stability of expansive rock is essentially controlled by the rock properties, geological structure, the expansion grade and ground water environment. The mineral composition and cementation strength between the rock and soil vary because of their different formation histories. The artificial rainfall tests have been carried out at the experimental canal slopes at the Middle Route of the South to North Water Diversion Project at Xinxiang, Henan Province. The characteristics of the deformation and slide characteristics are analyzed on the basis of the above tests. The test results show that the main characteristics of deformation and failure of expansive rock slop are the ditches formed by rainfall, slope heave, local shallow sliding, and that the primarily external factors are construction unloading, arid and semi-arid climates and precipitation. The research production is a basis to the engineering design and the investigation for the failure mechanism of the expansive rock slope.