I have add a blob property in my pagetype.Its accept the Unique Identifier.But I dont know What the Use of it in Editor's perspective?
You can hide properties in edit mode by using the ScaffoldColumn attribute, see http://joelabrahamsson.com/hiding-episerver-properties-from-editors/
Thanks and it worked. But still I am not sure about the use of blob property in admin area.
There is no use for it for editors. It's used for storing references to blobs, but an editor can't create blobs and then select them.
Right now that property type is only used internally by the product for MediaData to store references to uploaded blobs.