[firedamage]

why magnesium strip become powder,white colour and crispy after burned with oxygen?

[Arkcon]

Well, lets start with a balanced chemical reaction.  That's a better answer, chemically, for what's going on, than "criispyness."

[firedamage]

oxidation and reduction occur?this is a combination reaction.

[P]

What happens to everything else when you burn it in?

[Arkcon]

You do know the term for the type of reaction commonly refered to as "burning", I've seen you use it, in another thread, today.  Can you pull together what you know, to begin solving this problem?

[firedamage]

the flame burned vigourusly.