If I kill mobs by shooting with crossbow, the crossbow does not gain any experience
here is the crash report by holding f3 + C for 10 seconds:

crash-2017-12-23_18.56.05-client.txt

Ok, it worked, and I figured out why it doesn't work in my main world.: I forgot to change the old tinkers bolt into the new bolt that have levels.

Crossbows gain xp on hit, not on death. Weapons/Arrows gain xp on death. Are you in creative mode?

Yes I am in creative

The experience stayed at 0 no matter hit or kill

Go into survival. You don't have crossbow ammo on yourself, which is needed for it to work.