The hydrogen adsorptions on 2H-phased MoX2 (X= S, Se) monolayers as a function of biaxial strain or external vertical electric field were investigated on the basis of density-functional theory. The results show the intrinsic bandgap and electron transfer effects on the hydrogen adsorption of MoX2 monolayer, which reveal the relationship between the electronic structures of MoX2 and corresponding hydrogen adsorption behaviors. Both biaxial strain and external vertical electric field have the ability to change bandgap of MoX2 monolayer. Bandgap narrowing can lead to hydrogen adsorption strengthening. The hydrogen adsorption on MoX2 monolayer can also be finely tuned by an electron transfer between H adatom and substrate by means of vertical electric field. Therefore, we suggest that these two factors can possibly be regulated and synergistically tune the hydrogen adsorption on MoX2 monolayer.