The effects of the atomic motion and the field-mode structure, on the evolution of the linear entropy of the atom were examined in the Jaynes-Cummings model by means of linear entropy when the field was initially prepared in Schrdinger cat state and squeezed coherent state. It was found that the degree of entanglement between the atom and the field is very sensitive to the squeezing parameter. It was shown that the atomic motion leads to the periodic evolution of the linear entropy and an increase in field-mode structure parameter results in shortening of the evolution period of the linear entropy and decreasing in the amplitude of the linear entropy when the field is initially in Yurke-Stoler state. Furthermore, the increase of field-mode structure parameter leads to the shortening of the evolution periodicity of the linear entropy, but has no effect on the amplitude of the linear entropy when the field is initially in even coherent state.