Considering both the axial force on the spanning pipeline and influence of sea waves and currents, a perpendicular nonlinear vibration equation which satisfies given boundary conditions is set up according to the factual soil supports for the pipeline. Based on the inherent modes of vibration determined from the equation of motion describing free vibrations, the differential equations for the time domain of the equation solution are deduced and established. By the application of time and frequency domain analysis, the sea wave and current force spectrum is derived from wave spectrum and is used as the input spectrum of the vibration equation to deduce the output spectrum, and further determine the probability distribution of displacement and strain. On this basis, the fatigue invalidation probability of the spanning pipeline is found out according to the theory of reliability. Finally, by means of calculation and analysis of a practical sample, the degree of effect of some important parameters on fatigue invalidation of the spanning pipeline span is determined. Considering both the axial force on the spanning pipeline and influence of sea waves and currents, a perpendicular nonlinear vibration equation which given given boundary conditions is set up according to the factual soil vibration for from the the equation of motion describing free vibrations, the differential equations for the time domain of the equation solution are deduced and established. By the application of time and frequency domain analysis, the sea wave and current force spectrum is derived from the wave spectrum and is used as the input spectrum of the vibration equation to deduce the output spectrum, and further determine the probability distribution of displacement and strain. On this basis, the fatigue invalidation of the spanning pipeline is found out according to the theory of reliability. Finally, by means of calculation and analysis of a practical sample, the degree of effect of some important pa rameters on fatigue invalidation of the spanning pipeline span is determined.