The invention discloses a water-bath constant-temperature oscillator. The water-bath constant-temperature oscillator is technically characterized by comprising a bearing plate, wherein test tube holesare formed in the bearing plate; a test tube is inserted into each test tube hole; a filling part is filled into a gap between each test tube hole and the test tubes of different diameters so as to fasten the test tubes. The water-bath constant-temperature oscillator has the advantage that the easiness in shaking of the test tubes of different diameters is avoided in the oscillation process.