Abstract: Q420C steel plate for high heat input welding was developed by composition design and process design, and its welding performance were tested. The results show that the microstructure of the Q420C steel plate was fine and uniform with good mechanical properties. The impact absorption energy of the Q420C steel plate was more than 200 J at -80 ℃. When the heat input was 250 kJ·cm^-1, the impact absorption energy at the fusion line was much higher than the technical requirements, and the welding performance was good.