The large values and constituent-quark-number scaling of the elliptic flow of low-pT D mesons imply that charm quarks,initially produced through hard processes,might be partially thermalized through strong interac-tions with quark-gluon plasma (QGP) in high-energy heavy-ion collisions.To quantify the degree of thermalization of low-pT charm quarks,we compare the D0 meson spectra and elliptic flow from a hydrodynamic model to experi-mental data as well as transport model simulations.We use an effective charm chemical potential at the freeze-out temperature to account for the initial charm quark production from hard processes and assume that they are thermal-ized in the local comoving frame of the medium before freeze-out.D0 mesons are sampled statistically from the freeze-out hyper-surface of the expanding QGP as described by the event-by-event (3+l)D viscous hydrodynamic model CLVisc.Both the hydrodynamic and transport models can describe the elliptic flow of D0 mesons at PT ＜ 3 GeV/c as measured in Au+Au collisions at √SNN =200 GeV.Though the experimental data on D0 spectra are con-sistent with the hydrodynamic result at small PT ～ 1 GeV/c,they deviate from the hydrodynamic model at high transverse momentum,pT ＞ 2 GeV/c.The diffusion and parton energy loss mechanisms in the transport model can describe the measured spectra reasonably well within the theoretical uncertainty.Our comparative study indicates that charm quarks only approach local thermal equilibrium at small pT,even though they acquire sizable elliptic flow comparable to light-quark hadrons at both small and intermediate PT.