A variable diameter rotary test-tube oscillator comprises a base (1), a support plate (2), a motor (9) and a turning disc (3), a driving crankshaft (4) is disposed between the turning disc and the support plate, two ends of the driving crankshaft are inserted into the support plate and the turning disc respectively, a driven crankshaft (5) is also disposed between the turning disc and the support plate, the driven crankshaft is parallel to the driving crankshaft, two ends of the driven crankshaft are inserted into the support plate and the turning disc respectively, and an eccentric distance of the driving crankshaft is equal to that of the driven crankshaft. The eccentric distance may be adjusted as require to obtain suitable oscillational amplitude, test-tubes are uniform in rotation speed during rotation of the turning disc, and the test-tubes are equal in mixing effect. The variable diameter rotary test-tube oscillator is advanced in structure, uses few parts, is stable in turning disc running, low in operating efficiency and high in uniformity quality, solutions of the test-tubes are uniformly mixed, mixing efficiency is improved, and the oscillator is an ideal apparatus for mixing sample solutions in a chemical examination room or laboratory for sanitation industry, medicine industry, light industry, chemical industry and the like.