Monolayer transition-metal dichalcogenides (TMDCs) with intrinsically broken crystal inversion symmetry have shown large second-order nonlinear responses, providing a new platform for nonlinear light-matter interaction engineering. Integrating two dimensional monolayers with nanoresonators has been demonstrated to enhance the second harmonic generation. Previous designs suffer from the drawbacks of low cavity quality factor and/or small interaction area. In this letter, we demonstrate the enhancement of second harmonic generation by coupling a TMDC monolayer to the guided-mode resonances of a one-dimensional photonic crystal, showing a 170-fold enhancement of the generated signal relative to a bare monolayer. The work shows a way towards silicon chip-integrated nonlinear devices based on two dimensional materials.