[angelku]

I want to know the details of it.How to link it to the compound which have ketone and aldehyde functional groupin detm?

[Dan]

look up the structure of dnp (2,4-dinitrophenylhydrazine is the one you are talking about I presume?) and look up hydrazone formation. Hint: The mechanism is analogous to imine formation.

[angelku]

What would  happen with a compound which contain many aldehyde and ketone function group?
Is there any method to identify the unknown compound which either contains  aldehyde or ketone function group instead of treating it with 2,4-dinitrophenylhydrazine?

[angelku]

Why using fractional distillationis not a good method to identify the an unknown compound which have lots of ketone and aldehyde ?

I guess the smiliar boiling point of ketone and aldehyde which cannot easily to determine. Am I right?

[Dan]

What would  happen with a compound which contain many aldehyde and ketone function group?

You would probably get a mixture of products. Aldehydes generally react faster with nucleophiles than do ketones, but DNP can't (reliably) be used to distingush aldehydes from ketones.

Is there any method to identify the unknown compound which either contains  aldehyde or ketone function group instead of treating it with 2,4-dinitrophenylhydrazine?

Yes. Have a look at this website http://www.wpbschoolhouse.btinternet.co.uk/page13/ChemicalTests/ChemicalTests.htm

Why using fractional distillationis not a good method to identify the an unknown compound which have lots of ketone and aldehyde ?

I guess the smiliar boiling point of ketone and aldehyde which cannot easily to determine. Am I right?

Well you can't identify an unknown by its boiling point. Boiling point tells you very little about the structure.