Abstract: Three kinds of 800 MPa high strength steels with Ti and Nb precipitation strengthening and containing different Mo and B contents were weld under the conditions of mixed gas arc welding and heat input of 13 kJ·cm-1, and the microstructure, strength and hardness of the welded joints were studied. The results show that the heat affected zone (HAZ) of the high strength steel with lower Mo was found softening. With the increasing of Mo and B, which increased the hardenability characteristic, the hardness of HAZ increased and the tensile strength increased from 720 MPa to 760 MPa and 795 MPa, respectively. Adding Mo and B elements had no obvious affection on the behavior of second phase particle (Ti, Nb, Mo)(C, N) in HAZ.