Disclosed herein is an interface treatment method for germanium-based device, which belongs to the field of manufacturing technologies of ultra large scaled integrated (ULSI) circuits. In the method, the natural oxide layer on ther surface of the germanium-based substrate is removed by using a concentrated hydrochloric acid solution having a mass percentage concentration of 15%˜36%, and dangling bonds of the surface are performed a passivation treatment by using a diluted hydrochloric acid solution having a mass percentage concentration of 5%˜10% so as to form a stable passivation layer on the surface. This method makes a good foundation for depositing a high-K (high dielectric constant) gate dielectric on the surface of the germanium-based substrate after cleaning and passivating, enhances quality of the interface between the gate dielectric and the substrate, and improves the electrical performance of germanium-based MOS device.