  As the standard gamma-ray burst (GRB) prompt-emission model, the internal
shock (IS) model can reproduce the fast-rise and slow-decay features of the
pulses in the GRB light curve. The time- and energy-dependent polarization can
deliver important physical information on the emission region and can be used
to test models. Polarization predictions for the GRB prompt phase with the
magnetized IS model should be investigated carefully. The magnetic field of the
magnetized IS model is very likely to be mixed and decays with radius. The
synchrotron emission in the presence of such a decaying magnetic field can
recover the Band-like spectrum of the GRB prompt phase. We investigate the
dependence of the polarization of GRB prompt emission on both time and energy
in the framework of the magnetized IS model. Due to the large range of
parameters, it is hard to distinguish the magnetized IS model and the
magnetic-reconnection model through polarization degree (PD) curves. The
energy-dependent PD could increase toward the high-energy band for the
magnetized IS model, while it decreases to zero above the megaelectronvolt band
for the dissipative photosphere model. Therefore, we conclude that the energy
dependence of PD can be used to distinguish these two models for the GRB prompt
emission. Finally, we find that, independent of the observational energy band,
the profiles of the $\xi_B-PD$ curve for the time-integrated and time-resolved
PDs are very similar, where $\xi_B$ is the magnetic field strength ratio of the
ordered component to the random component.
