Piezoelectric polymer foams (Piezoelectrets) are space-charged porous materials with a wide range of applications. Mathematical models have been developed to understand the influences of the porous structure on the piezoelectric properties. These models omit the details of the pore structures and their effects on the mechanical and electrical characteristics, limiting the capability to qualitative prediction only. In this paper, an electro-mechanical coupled model was established for quantitative prediction of the piezoelectric properties of 3D printed piezoelectrets. The model takes into consideration of the pore structures details and their deformation, the accompanied charge development, and their coupled effects. To validate the model, a series of piezoelectrets with pre-defined structure parameters were designed and 3D printed using fused filament fabrication (FFF). Their piezoelectric properties were characterized. The model calculated piezoelectric coefficient d33 of piezoelectrets were in excellent agreement with the experimentally measured values. We finally demonstrated the excellent quantitative predictive capability of the model by using an out-of-sample set of piezoelectrets. The developed model can be used to guide the design of piezoelectrets structures for desired piezoelectric performance.