We use the full-density matrix numerical renormalization group method to calculate the equilibrium dynamical corre-lation function C(ω)of the spin operator σz at finite temperature for the sub-ohmic spin-boson model.A peak is observed at the frequency ωT～T in the curve of C(ω).The curve merges with the zero-temperature C(ω)in ω>>ωT and deviates significantly from the zero-temperature curve in ω<<ωT.