The simulation of shielding properties of gradient composite structures (g-CMs) nanocarbon-polymer in the frequency range of electromagnetic radiation (EMR) (25.5 - 55.5GHz) has been implemented in C++ code. The simulation has shown a significant decrease of EMR reflection index (R) and sufficient increase of EMR absorption (A) and shielding efficiency in gradient composite structures with filler concentration growth in the direction of EMR propagation as compared with composite with uniform distribution of nanocarbon filler. The simulated results coincide with the experimental data for the set of the epoxy composites with gradient distribution of 5wt.% of graphite nanoplatelets.