By using the multiphoton Jaynes-Cummings model,the dynamical properties of the field entropy in the system that consists of a two-level atom interacting with a single-mode field via multiphoton transition are studied.The frequency of the field varying with time in the form of u sin wt has been considered.The results show that the time-evolution behavior of the field entropy is modulated by the frequency variation of field using the numerical.The modulation intensity is enchanced as the amplitude u of frequency variation of field increases.When the amplitude u of the time varying fields is larger than a fixed value,the time-evolution behavior of the field entropy will display periodic oscillation behavior.Its oscillation period agrees with the period of frequency varying.It shows that the evolution of field entropy is influenced by the frequency parameters w and u of the field varying with time.