Abstract: From the starting of the queue length process itself,this paper directly studies the distribution of the queue length in the M/G/1/∞ queueing model by using the Laplace transform tool.The recursion express of the Laplace transform of the transient queue length distribution at any time t and the recursion formula of the equilibrium distribution for calculating conveniently are obtained.At last some more useful recursion formulas for calculating are given in several special queueing models.