In this paper an enhancement of second harmonic generation efficiency which radiated from MoS2 monolayers embedded in one-dimensional photonic crystal structures is studied. The system contains air, SiO2 and MoS2 layers in periodic manner with the same thickness of air and SiO2 layers. The transfer matrix method is used for calculating the forward and backward second harmonic generated wave efficiencies in undepleted pump approximation. Our results show the giant enhancement of second harmonic generation efficiencies up to seven orders of magnitude only with N = 40 MoS2 monolayers in the system. The results are obtained by tuning the thickness of air and SiO2 layers at about 1284nm for fundamental wave of  810nm wavelength. Choosing the above thickness causes the second harmonic waves, generated in each MoS2 monolayers, to interference constructively. Both of the fundamental and second harmonic wavelengths are located at the photonic band gap edges where the density of electromagnetic modes and the nonlinear interaction time are enhanced. These two mechanisms help us to improve the second harmonic generation efficiencies. Increasing the segments numbers enhanced the overall thickness of MoS2 nonlinear layers which affect the phase matching conditions and decreased the SH efficiencies.

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