The offshore platform tubular joint fatigue life reliability prediction was achieved by employing the  Liouville probability density evolution equation to obtain the fatigue crack probability density function (PDF). In this method the statistical characteristics of alternating stress stochastic process was gained by combining frequency domain and time domain calculation. The expansion method of stochastic processes based on normalized orthogonal bases was employed to expand alternating stress stochastic process as linear combination of time functions and independent random variables. The crack propagation rate equation was converted into the first class of stochastic differential equations in order to set up the Liouville probability density evolution equation, and the numerical analysis method was employed to solve it. The example verified the validity and simplicity of the proposed method.