Finite element analyses were conducted on a three-phase piezoelectric nanocomposite to investigate the effects of several design parameters on performance. The nanocomposite consisted of a polyimide matrix enhanced with single-wall carbon nanotubes and PZT-5A particles. The effective piezoelectric properties were computed for a wide range of nanotube and PZT particle concentrations. A discrepancy was found between the experimental and computational results. Several modified finite element models were developed to explore possible reasons for this discrepancy, and a hypothesis involving nanotube dispersion was proposed to explain the difference. The response of the nanocomposite under harmonic loading was also investigated using the finite element model. It was found that increasing the dielectric loss of the matrix enhanced piezoelectric performance up to a certain point, which could be an effective tool in designing piezoelectric composite materials.