Abstract: The wall electrode sensors have been widely used in the measurement of transport process.However,the theoretical equations in prior work did not include the effect of mass transfer to the edge of wall probe.This effect will bring an important contribution to the electrode current if the probe is small enough,which a lager measuring error if the original equation is used.This paper gives some modified equations in which the effect of mass transfer to the probe edge is considered.The experiment results pressented have supported these equations.