It is essential to adopt the welding fabrication which assures high level of soundness of the welded joint in welding high performance structures such as submersible vessel made of steels with both high toughness and high tensile strength. In that case, it is important to prevent weld cracking which affects the soundness of welded joint. Therefore, the authors carried out various weld cracking tests for butt joint and fillet joint of steels with high toughness and high tensile strength to be used for pressure hull of submersible vessel, and investigated the effect of water content in flux of electrode and ambient humidity on the weld cracking behavior from the viewpoint of welding fabrication. On the basis of the investigation, the conditions for preventing weld cracking were established.