In this paper, creep analysis of a thick-walled spherical pressure vessel made of Functionally Graded Material (FGM) under thermo-mechanical loadings has been investigated based on Bailey-Norton Law. Considering the nonlinearity of the creep behavior, there is no analytical solution that can accurately determine the stresses of an FGM as a function of time and thermal boundaries, thus in this paper, a new method based on the Taylor Series expansion of the creep strain rate is developed to solve the Beltrami-Michell equation by employing an asymptotic method. The resulting quantities are compared with the numerical ones and show good accuracy. The impacts of FGM constants and wall-thickness, and series order on the creep stress and strain distributions are evaluated. The results are depicted graphically and reveal that even for vessels with high wall thickness and FGM constants, the proposed method equipped with high orders of the Taylor series produces accurate results. Also, due to the agreement of both numerical and analytical methods, this method can be generalized to study the creep of other symmetric FGM structures. Manuscript profile