Welding efficiency is very important for offshore platforms and ships, and non-preheat welding can improve welding efficiency and reduce costs. In this paper investigates the effect of Si content of welding rods on the microstructure and performance of welded joints of 690 MPa low alloy high strength steel welded by electrode arc welding without preheating. Research has found that the Si content of the welding rods has an important effect on the microstructure, phase transformation process and strength and toughness of the welded joints. Under certain conditions, reducing the Si content of the welding rod can refine the microstructure of the welded joint, obtain good toughness of the welded joint, so that the welded joint performance to achieve a tensile strength of 700 MPa, the impact absorption energy at −50 ℃ is 142-159J (average value 148J).