I was getting duplicate data in database while refreshing the page in Registration page. I searched on asp.net forum. Then i got the two type of solution
1. After insert operation just redirect to that page
protected void BtnSubmit_Click(object sender, EventArgs e)
//code for insert
2. Using sql query, before inserting into database, we have to check that record in database . If that record is available in database stop the execution of code.
For more detail,Please read this article