Deathclaws are fast and have a ferocious melee attack so keep your distance.
You will need to be wearing a Power Armor as this has increased damage and radiation resistance. You get this whilst doing the "When Freedom Calls" quest for Preston Garvey on the roof of the "Museum of Freedom" in Concord. On that quest you will get the minigun which is next to the armor, use that too.
Use V.A.T.S (Q) to slow down and aim the minigun at the torso and head and queue up shots, then retreat backwards and repeat.
There is a shop on the left opposite the museum you come out of and this can be used for cover, trying to shoot him (with V.A.T.S engaged) through the windows.
You can even try to shoot him from the roof of the museum but he runs away and takes ages to return but you can at least weaken him a bit before you go down onto the street to fight him.