Conditional distribution reflects the dependency link among random variables, but two-dimensional random variables Conditional Distribution has some limitations. In order to rich the content of conditional distribution this paper gives the extension of conditional distribution under discrete random variables and some examples. This article obtains the extension strictly in accordance with the definition of two-dimensional random variables. So it can get conditional distributions after changing the condition and get conditional distributions that are extended into n-dimensional random variables, thereby enriching the contents of the conditional distribution.