Abstract: Based on Ni-Cr-Mo-V alloy system, the effect of yttrium oxide on microstructure and mechanical properties of weld made with 800 MPa high strength steel electrode was investigated. Experimental results show that, as the Y₂O₃ content changed in 0~0.02%, with the increase of Y₂O₃ content, the proeutectoid ferrite content reduced, the acicular ferrite content increased, and the strength and low-temperature impact toughness increased gradually. When the Y₂O₃ content was 0.02%, the low-temperature impact toughness of weld metal reached the maximum. When the Y₂O₃ content was over 0.02%, the acicular ferrite content in the weld reduced, and the low-temperature impact toughness decreased. Therefore, the optimum Y₂O₃ content for high strength steel electrode is about 0.02%.