Ferromagnetic resonance experiment was performed to study the variations of micromagnetic structure with heat treatment of melt spun $Fe_{76}Cu_{1}Nb_{3}Si_{14}B_{6}$ alloy for 1h at every $50^{circ}C$ in the temperature range of $400^{circ}C-700^{circ}C$. The variations of micromagnetic structure was discussed qualitatively in terms of the variations of line width ${Delta}H_{p-p}$ and resonance magnetic field $H_{res}$. With increasing armealing temperature to $400^{circ}C$, ${Delta}H_{p-p}$ decreases and $H_{res}$ increases due to the decrease in magnetic anisotropy resulting from structural relaxation during heat treatment. With increasing annealing temperature from 400 to $500^{circ}C$, ${Delta}H_{p-p}$ increases and $H_{res}$ decreases due to the increase in magnetic anisotropy resulting from the formation of nanocrystalline particles embedded in an amorphous matrix. With increasing armealing temperature from 500 to $550^{circ}C$, ${Delta}H_{p-p}$ decreases and $H_{res}$ increases due to the decrease in magnetic anisotropy resulting from the formation of homogeneous nanocrystalline structure with a minor amorphous phase. Further increase in armealing temperature above $550^{circ}C$ C causes ${Delta}H_{p-p}$ to increase and $H_{res}$ to decrease due to the increase in magnetic anisotropy due to the formation of inhomogeneous grain structure and intermetallic compounds.