Did you get some good document how to calculate MTBF for clock domain crossing ?"I want a document of MTBF for clock domain crossing analysis ? "
You are mixing concepts. Maybe you are talking about metastability? This has nothing to do with reliability.
As for lucbra recomendation, MIL-HBK-217 will give you a very pesimistic number. I do not know the details but there are other references which are well accepted by the worlwide realibility experts. I will try to find the info and get back