The effect of thermal fluctuations in the resonance fluorescence of a three-level system is studied. The damped three-level system is driven by two strong incident classical fields near resonances frequencies. The simulation of a thermal bath is obtained with a large system of harmonic oscillators that represent the normal modes of the thermal radiation field. The time evolution of the fluorescent light intensities are obtained solving by a iterative method the Heisenberg equations of motion in the integral form. The results show that the time development of the intensity of the fluorescence light is strongly affected by the interaction of the system with the thermal bath.