The invention discloses a telescopic nozzle device for narrow gap welding and an adjusting method of the telescopic nozzle device. The nozzle device sequentially comprises a nozzle holder, an air sifter cover, a locking nut, a gas calm sleeve, a telescopic adjusting nut and a movable nozzle sleeve from top to bottom, one end of the gas calm sleeve is fixedly connected with the nozzle holder through the locking nut, the other end of the gas calm sleeve is in transmission connection with the telescopic adjusting nut through a thread pair, the movable nozzle sleeve can vertically move along the axial direction of a nozzle under driving of the telescopic adjusting nut, so that the extending length of the movable nozzle sleeve is changed, and the overall axial length of the nozzle is telescopically adjusted. The telescopic nozzle device is compact in structure, convenient to telescopically adjust and wide in effective gas protection range, an inner cavity of the nozzle is fine in gas tightness, and gas protection can be provided for welding seams with different depths in narrow gap grooves.