The utility model discloses a simple rail geometrical parameter measurement instrument which comprises a cross beam, wherein a short beam is arranged at one end of the cross beam and is perpendicular to the cross beam, the two sides of the short beam are respectively with a fixed end positioning wheel component and a fixed end traveling wheel component, the fixed end traveling wheel components are fixedly connected with the short beam through the fixed end positioning wheel components, a movable end positioning wheel component and a movable end traveling wheel component are arranged on the side, away from the short beam, of the cross beam, the movable end positioning wheel component is arranged on the cross beam through the movable end traveling wheel component, a handle used for controlling the movable end positioning wheel component to stretch and retract in a sliding mode is arranged on the cross beam, and the handle is connected with the movable end positioning wheel component through a pulling connection line. According to the instrument, measurement gauge is adjustable so that different gauge requirements can be met, and measurement data are true and reliable; meanwhile, the structure is stable, the cross beam and the short beam are connected through a reinforcing rib plate structure, and structural stability is improved.