To provide a narrow-groove gas-shield arc welding method of a thick steel plate, in which a generation position of welding arc is accurately controlled, penetration of a groove bottom is sufficiently secured, and weld defect is prevented.

In the narrow-groove gas-shield arc welding method: a power source having drooping characteristics or constant current characteristics is used to control an arc voltage to thereby control the generation position of an arc; furthermore, a welding current and the arc voltage are synchronized to be controlled; if needed, a welding speed is synchronized with the arc voltage to be controlled, and a welding heat gain and a welding quantity are controlled; and an average welding current is 500 A or higher. In a multielectrode gas-shield arc welding using two or more electrodes, the narrow-groove gas-shield arc welding method is applied to the subsequent electrodes of a second electrode.