Provided is a small deformation wind tunnel train balance, comprising a rod-type balance and a support pole. Two ends of the rod-type balance have a conical structure. A balance element is arranged between the two ends of the rod-type balance. The balance element has a conical structure, which is provided thereon with a five-component element adjacent to the large-end part and a resistance element adjacent to the small-end part. The support pole comprises a conical front end and a straight segment. The rod-type balance and the conical front end of the support pole are matched via a conical surface and are tensioned via a wedge. The rod-type balance is arranged in an inner cavity of a tested model. The minimum diameter of the inner cavity of the tested model is greater than the maximum diameter of the rod-type balance. The invention breaks through the traditional equal-diameter balance support rod design method and the three-segment type rod-type balance structure, increases the diameter of the balance, shortens the balance length, realizes little deformation of the balance, improves the rigidity and the bearing ability of the balance, is applicable to balance development for wind tunnel experiments with large impact load or severe vibration, and achieves good practicability and popularization values.