A fixture for machining wheel outer rim without trace includes a positioning and clamping portion and a flexible support portion. A base is fixed on a bottom plate, and a screw is configured to compress an expanding pressure plate during being tightened so that the outer circumference of an expanding sleeve expands a center hole of a wheel; and the positioning columns are inserted into bolt holes of the wheel. A lower pressure plate is fixed on the base, and limiting columns and an upper pressure plate are installed on the lower pressure plate, with steel balls and rubber strip being enclosed in a space formed by the lower pressure plate and the upper pressure plate. The fixture meets the requirement for machining the wheel outer rim without trace, has the characteristics of simple structure, convenient manufacture, stable performance and precision, and meets the requirements of automatic production.