The influence of porosity and magnetic field on a mathematical model of functionally graded piezoelectric (FGP) hollow structures (cylinder and sphere) in a hygrothermal environment is presented using a semi-analytical technique. The mathematical model is under the effects of many forces, in addition to a magnetic field, which is still a challenging study. Loading is a collection of mechanical pressure on the inner and outer surface, magnetic field, hygrothermal influences, and change of electric potentials between external and internal surfaces. The whole material properties are supposed to be a polynomial function of radius. Numerical results discuss four different boundary conditions for each model of mechanical pressure and electric field subject to the influence of temperature, humidity, and magnetic field. To check the numerical results, the results are compared between functionally graded porous and non-porous hollow structures. In the end, numerical outcomes clarified the influence of the porosity factor in the mathematical models and its importance in mechanical engineering and modern technology.