The invention relates to the technical field of triaxial test devices, and discloses a voltage stabilizing mechanism, a mechanical rheological experiment system and a test method thereof. The voltagestabilizing mechanism comprises a pressing rod and a piston. The end part of the piston is slidably arranged on the pressing rod. One end of the pressing rod is provided with a base hinge part, so that the pressing rod can rotate up and down. The other end of the pressing rod is provided with a force applying part. According the invention, the voltage stabilizing mechanism has the advantages of simple structure and quick and convenient operation; disadvantages caused by electric control voltage stabilizing are avoided; the stability of a loading force is ensured; the mechanical rheological experiment system of the voltage stabilizing mechanism can eliminate the problem of unstable loading force caused by voltage instability under traditional electric control; the test result is more stableand accurate; and the voltage stabilizing mechanism, the mechanical rheological experiment system and the test method can be applied to various triaxial tests.