We have performed structure searches for titanium (Ti) hydrides, vanadium (V) hydrides, zirconium (Zr) hydrides and niobium (Nb) hydrides under ambient and high pressure up to high hydrogen content using CALYPSO method combined with first-principles calculations. Ten novel stable phases, R (3) over bar -TiH3, P4(2)/mnm-TiH3, Ibam-TiH2.5, Cccm-VH, Pna2(1)-ZrH4, R (3) over bar -ZrH3, Pm (3) over barn_1-ZrH3, R (3) over barm-ZrH2.5, P2/c-NbH2.5 and P4(2)/mcm-NbH2.5 were discovered under various pressures. In particular, the high hydrogen content Pna2(1)-ZrH4 can be stabilized at 4-12 GPa. The detailed crystal structure, dynamical stability and electronic structure are also investigated for those novel stable phases. Combined with earlier predicted structures, comprehensive pressure chemical potential (P-Delta mu(H)) phase diagrams are constructed for these M-H systems. (C) 2019 Hydrogen Energy Publications LLC. Published by Elsevier Ltd. All rights reserved.