I am having trouble catching this Pokemon, it just keep on fainting every time we fight.
Yeah, there is.
Remember, using Super Effective moves at the beginning and not very effective moves later on helps.
Try to use the move False Swipe, It whittles down Pokemon but keeps a Pokemon at 1 HP. Inflicting a status move like Paralyzing will help too, so try to whittle it down as much as possible and throw lots of balls!