This paper is intended to desctibe a method for the efficient representation of the probability density function of a population by the variation diminishing spline function. The variation diminishing spline functions have two advantages : 1)They have the"shape-preserving" properties. 2)They are represented by a few knots and nodes. From these advantages, they are suitable to represent the probability density functions, and the mean and the variace are easily calculated by a few knots and nodes.