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in this work, we model the transient absorption of attosecond pulses of laser-dressed atoms by considering a three-level system.We study the delay-dependent interference features in the transient absorption spectra of helium atoms from the perspective of the interference between the attosecond pulse and the quasi-harmonic spectrum with the adiabatic approximation, and find that many features of the interference fringes in the absorption spectra of the attosecond pulse can attribute to the changes of the coherence phase difference.And we also find the sideband signal of the dark state is related to the the dark state with population modulated by the dressing field.