Non-uniform structures and composite materials have advantages in engineering appli-cations, such as light weight design, multi-functionality, and better buckling/flutter load capacity. For composite structures under dynamic loading conditions, reliability is a key problem to be analyzed during practical operations. However, there is little research work on non-uniform composite structural reliability analysis under random load. The forced vibration response of non-uniform composite beam under random load is firstly solved by the Adomian Decomposition Method (ADM) and iterative process for reliability analysis. Different variation laws of the cross-section rigidity and mass distribution along the length of the non-uniform composite beam structures are analyzed. Various angular frequency and amplitude of random base motion acceleration following Gaussian distribution are considered. Influences of different random excitations and structural design on vibration responses and reliability are studied. The larger mean and variance of excitation frequency leads to the smaller amplitude and strain of the beam, while greater mean and variance of the base motion excitation amplitude will induce the higher maximum amplitude and strain values and lower reliability. The influences of structural design on reliability are studied. The reliability increases with the increment of taper ratios of the host beam and composite layer. The iteration mathematical model and numerical solutions proposed in this paper can be used to solve and analyze vibration responses and reliability of general non-uniform composite beam structures under arbitrary excitation during a certain period of time.