Abstract: Based on the EH36 high-strength ship plate steel,the effects of welding heat input on mechanical properties by tensile and impact test in submerged arc welding process were investigated in the paper.The microscopy-shaped of fracture was also analyzed by scanning electron microscope(SEM).The results showed that all the fracture occurred in base metal.In the large heat input welding condintions,the strength of joints and heat affected zone(HAZ) was better than that of the base metal and no softening phenomenon in HAZ.The impact toughness of joint decreased as the welding input increased.The fracture morphology of weld and fusion zone was the mixed fracture for toughness and quasi-cleavage fracture.With the distance from the fusion line increased,the impact value tended to increase.The impact value was close to the value of base material at distance of 4 mm away from the fusion line which indicated the toughness of this position was not affacted by welding heat cycle.