The complex modal approximate analysis is developed to the vibration of foundation beams, studying transverse vibrations of three-parametric viscoelastic Pasternak foundation beams. Complex frequency equations and modal function expressions are obtained for clamped-clamped，clamped-pinned and free-free ends. The numerical methods are employed to approximately solve the transcendental equations, and the differential quadrature scheme is applied to verify the approximate result. The effect of the boundary conditions, the stiffness and the viscoelastic coefficients on natural frequencies and modal functions are analyzed in numerical examples. The numerical results obtained with the differential quadrature and the complex mode methods are in good agreement.