This paper presents a novel energy method for vibration analysis of pre-loaded moving functionally graded material (FGM) plates in fluid. Porosity in plates, fluid–structure interactions and initial tensions are taken into consideration. The first-order shear deformation theory (FSDT) and linear potential flow theory are adopted to formulate the strain energy, kinetic energy and external work functions of the coupled system. The governing equations of the porous FGM plate immersed in liquid are deduced by the Hamilton’s principle and the unified solutions for general boundary conditions are obtained using the modified Ritz method. By comparing the obtained vibration results with those from the commercial software and literature, the accuracy of the proposed model is validated. The effects of axial speed, fluid density, material constituent, initial axial tension and porosity volume fraction on the vibration behaviors of the FGM plate are further discussed. Numerical cases show that the vibration behaviors of the FGM plate are significantly influenced by these key parameters.