Aim at the wheel diameter difference problem, influence of wheel diameter on wheel-rail contact geometrical relationship, contact spot, the maximum contact stress, creepage, vehicle stability and wheel-rail abrasion was researched. The result of calculation showed that with the increase of wheel diameter: left and right wheel rolling radius difference increased, and the equivalent conicity gradually increased with the wheel sliding; the contact spot area became large and the maximum stress decreased significantly; the wheel rail lateral and longitudinal creepage gradually decreased; the stability of the vehicle became better, and the wear became larger when the vehicle was over the curve.