The invention relates to a vehicle-deflection preventing catch wheel for a roller test bench and adapted to wheel location and tire diameter automatically, mainly including that: a ground guide rail portion is fixed on the ground, a sliding plate of a sliding plate portion is slideably matched with the ground guide rail portion; a worm wheel decelerator of an electrical motor worm wheel decelerator portion is driven by an electrical motor, is fixed on the sliding plate, and is meshed, via a gear over an output shaft thereof, with a rack that is fixed on a ground guide rail soleplate; a speed regulating motor and a ball screw portion are mounted on the sliding plate, the speed regulating motor drives the ball screw to rotate, a ball screw nut in a rotary arm portion is movable over the ball screw, a fork-shaped rotary arm rotates around a rotary shaft of a square screw nut sleeve that clamps the ball screw nut so as to cause a bearing rotary shaft in a bearing support to rotate, and tocause the catch wheel and the catch wheel in sensor portion to rotate. The inventive objective lies in a technical proposal that is proposed for the purpose of chiefly solving unstable operation of current front-wheel driven vehicle on the roller test bench.