The utility model discloses a rainfall system for an open pit mine slope similarity simulation test. Slope model module, Rain simulation module, Wind module and water storage module, the side slope model module comprises a side slope heap; Model frame, the side slope heap is placed in the model frame; the rainfall simulation module comprises a rainfall water tank; the rainfall water tank is arranged on the slope heap and is mounted at the top of the model frame; wherein the rainfall water tank is provided with a groove for containing water, a plurality of rainfall holes are formed in a bottomplate of the groove, the water storage module comprises a water tank and a main water pipe, the water tank stores water into the rainfall water tank through the main water pipe, the air module comprises a fan, and output air of the fan penetrates through the position between the rainfall water tank and a side slope heaping object. The slope structure and rainfall are simulated, water is in a raindrop falling shape when flowing out of the rainfall holes, the difference between the raindrop falling shape and jet simulation is distinguished, meanwhile, wind power in natural rainfall is simulatedthrough the fan, simulated rainfall is more real and reliable, and slope deformation under the rainfall condition can be ideally simulated.