Based on the Von Neumann quantum reduced entropy theory, the evolution properties of field quantum entropy in the interaction system of Λ-type three-level atom and single-model field are investigated when the coupling between the field and the atom changes with time and intensity under the on-resonance condition. The influences of the different initial fields and changes of the coupling coefficient on field quantum entropy is discussed in detail through numerical calculation. Results show that the different statistical properties of the initial fields will lead to the great variation of the field quantum entropy, and the changes of the coupling strength modulation function will change the oscillating frequency of the field quantum entropy evolution. In addition, it is shown that the initial stage of the interaction between the field and atom is a gradually coupled procedure, and the superposition state probability of the atom makes the field quantum entropy change periodically.