The invention relates to a side slope mining model testing device and method under the action of surface and underground water, which can effectively meet experiment requirements, improve experimental efficiency and greatly facilitate experimental operation and is high in comprehensiveness. The device comprises a vertical baffle wall with holes and a vertical side slope base plate with holes; the side slope base plate with holes is arranged on a device base; a steel frame is arranged outside the vertical baffle wall with holes and the vertical side slope base plate with holes; visible glass is installed around the steel frame; a lane opening is formed in the front side of the steel frame; side slope soil is arranged inside a space formed by the whole steel frame; a vertical counter force rack is installed on the outer side of the steel frame; a rainfall simulation device is installed at the upper part of the vertical counter force rack; a ground stress simulation jack is further arranged on the inner side of the vertical counter force rack; the vertical baffle wall with holes and the side slope base plate with holes are respectively connected with a corresponding lifting water supply device; and the steel frame and the vertical baffle wall with holes are respectively connected with a support device.