The SAW with large heat input（50 k J/cm） is used for automatic welding of F460 Z high strength steel with CHW-S3 AB wire and CHF102 flux. The mechanical prope-rties,microstructures and fracture morphology of the welded joints are researched. The results show that when the welding parameters are wleding current of 750 A,welding voltage of 39 V,welding speed of 33.3 mm/min,and preheating temperature at 180 ℃,the optimal joint is obtained,and its tensile strength is 583 MPa. The impact absorption powers of weld,bond line and HAZ at-60 ℃ are 55 J,62 J and 71 J respectively. The weld microstructure is mainly composed of acicular ferrite,and all indexes of welded joint meet the standard requipments.This provides theoretical and experimental basis for the application of SAW with large heat input in ocean engineering.