This paper investigates the effect of wall distance coordinate on predicting variable property flows with two-equation turbulence models. Three of five different definitions of wall distance coordinate are employed: the wall-property definition, the integral-property definition and the local-property definition. Three different two-equation turbulence models that involve the wall distance coordinate are tested against the varying property flow: Superheated gas flow. The definition of wall distance coordinate affects the size of the viscous region. The wall-property based unit makes the wall distance to be the smallest and contributes to widen the viscous damping region, so that the skin friction factor and the Nusselt number is lowered. All the predictions with three different wall distance coordinates lie within less than 20% in the calculated Nusselt number.