Abstract: Functionally graded materials (FGMs) are composed of two or more discrete constituent phases with continuous and smoothly varying components. Due to the distinctive merit comparing with usual composite materials that they can reduce the stress concentration and optimize the stress distribution to make good use of each component, utilizing of FGMs helps to resolve some problems in composite materials such as low bond strength and inharmonious of properties effectively. Because of the preparation technology or for the need of special structures, micropores or pores are commonly found in various types of FGM and play an important role in the influence factors on mechanical properties of FGMs. In addition, the application conditions of FGMs are usually complex or extreme with multiple physical fields, and the mechanical responses of various FGMs under coupling multi-fields will be more complex. On micro scale, the pores in porous FGM include material pores of each components and structural gaps between different particles. These pores will affect the properties of FGM, especially under hygrothermal environments. In this paper, two kinds of micro pores (material pores and structural gaps) in FGM are both considered. An expression to characterize porosity of the whole FGM is proposed, where the porosity of each component is related to its volume fraction and the global porosity is a linear superposition. Considering temperature dependency of the component properties as well as the material properties of pore fillers (liquid water or vapor), a prediction model of the porous FGM is established. Focusing on a rotating circular plate with its thickness varying along the radial direction, and applying the current porous FGM model, governing equations of the nonlinear steady-state temperature and moisture fields as well as displacement field are derived. Solving the governing equations by the differential quadrature method (DQM), distributions of temperature, moisture, displacement and stress of the FG circular plate are obtained. In the numerical examples, analytic solution of a simplified mechanical model is carried out to verify the numerical calculation process of the current study. By changing the key parameters, influences of each porosity, gradient index and thickness change rule on the hygrothermal mechanical responses of the porous FG circular plate with variable thickness are discussed in detail.