Abstract: The microstructure and mechanical properties of weld metal were influenced by base metal when the interaction crystallization and the composition dilution occur. The influences of oxide particles and Niobium on the microstructure of weld metal with high heat input welding and its impact toughness were studied. The results showed that the oxide particles can be transited to the weld metal and promote the formation of acicular ferrite in weld metal. Niobium elements can refine the grains of fusion line and decrease the width of columnar crystal in the weld zone. Compared with the parent metal without oxide particles and Niobium, the parent metal with oxide particles and Niobium can form the weld metal with higher toughness. Therefore, the influence of the base metal must be considered in selecting welding material.