The invention discloses a test device and method for simulating the seepage condition of the landslide of an earth-rock dam. The test device comprises a test chamber, a water inlet system, a flow leakage simulating system, a measuring system and an earth-rock dam model, wherein the earth-rock dam model is located in the test chamber; the water inlet system is located at the upper part of the left side of the upstream side of the test chamber, and is used for importing experimental water; the flow leakage simulating system is located at the bottom of the test chamber, and is used for simulating a flow leakage process under various working conditions; and the measuring system comprises a control box, an upstream water level gauge, a downstream water level gauge, an electric survey electrode, an osmometer, a connecting line, a control box platform and a water level gauge platform, and is used for realizing real-time measurement of various monitoring data. According to the test device disclosed by the invention, the landslide process of a side slope under the condition that the water level is suddenly changed can be truly simulated; dynamic monitoring of the change of the seepage condition is realized; and dynamic space seepage condition information is provided for the research on the change of instantaneous seepage conditions of the landslide under the condition that the water level is suddenly changed.