By using the method of dreessed atom of Dioke states, the master equation of resonance fluorescence in a three-atom system has been. The spectral construction of resonance fluorescence in the system has been found the ratio of weight of intension and relaxation rate of the spectra are calculated. It is found that the resonance fluorescence in a three-atom system consists of seven lines and each line has its own fine construction. We suppose that the reason of the splitting lies in coupling of the dipole momentes of dressed atom.