(Fe65Co35)x(SiO2)1-x granular films with various volume fraction (x) of Fe65Co35 alloy were fabricated by magnetron sputtering, and the interaction between granules was explored by δM(H) plots. Research results show that δM(H) is positive for the samples in a wide range of 0.42≪x≪0.86, indicating that exchange coupling exists among granules. Further research revels that δM(H)max increases gradually with decreasing x, reaching the maximum value at x=0.57, then decreases after x≪0.57. Since δM(H)max can effectively reflect the intensity of exchange coupling, the intergranular exchange coupling also increases first, then decreases as x decreases. The microstructure is analyzed with help of the high-resolution transmission electron microscopy, and results show that the variation of exchange coupling with metal volume fraction x is dominated by the change of microstructure of samples. The microstructure of the sample with x=0.57 satisfy the optimization for realizing exchange coupling, leading to excellent soft magnetic properties.