I have created dynamic string builder..now i want to fetch checkbox id from this string builder & wanna check these are selected or not.

This is not a good question - we cannot work out from that little what you are trying to do.
Remember that we can't see your screen, access your HDD, or read your mind.
That makes no sense as a question. We have no idea what you have put in your string builder, or what you want to do with it to fetch a checkbox id...
Use the "Improve question" widget to edit your question and provide better information.

What do you mean by a dynamic StringBuilder? Please show some code, because as it is your question is far from understandable.

OK. Where are you stuck? Loop through your checkboxes and compare to the values in string builder.

If you are asking how do you parse (read) the content of a StringBuilder, and retrieve values that you use to determine the state of a CheckBox, then we need to know what the format of the content of the StringBuilder ... is.