In a Λ-type electromagnetically induced transparency system, it shows that on the Doppler-broadened linear absorption background, as the probe intensity increases, the single narrow line-width window gradually evolves into 3 windows and 2 absorption peaks alternately. In this paper, the mechanism of probe intensity is studied in detail by using the dressed-state model. We propose that when the probe field is not so weak, the atomic Raman coherence can be manipulated by its intensity. For a Doppler-broadened system, there will appear the discontinuous energy variation of the dressed-states, and the large Raman loss due to the double resonance for dressed-states, which are the key factors for the evolution of the transparency window.