I can't defeat alduin in skyrim [closed]

Alduin is a beast of a dragon for sure and at level 11 you are not really going to have much in the way of stats. You will want to invest (look in shops) for resistance potions for Fire and Magic resistance. Both will help reduce the overall damage his magical attacks will cause to you. Secondly to help with the lower stats consider the HP boosting potions, not the ones that actually restore health but the ones that give you a higher maximum amount for a short while. Lastly, I am not sure what weapons you are using but I would consider using ranged weapons. Dragons have a very nasty habit of being able to pick up a person and just chomp em dead in a death animation, no way to get out of it game reloading sort of manner.

And the very ultimate thing you can do is just change the difficulty of the game. If you do not want to go try and better prepare for the combat or are incapable due to saves and such this may really be your only option. Difficulty can be changed even in the middle of combat and while it will not lower the level of what you are directly facing, it will reduce its impact upon your character and followers.

I would wait till level 20 and get the lovers stone. Have at least some kind of weapon enchantment and use a shield to bash him then attack and repeat.