foreach (DataRow dr in GridView1.Rows)
{
// assumed that you have four columns in your gridview
string t1 = dr[0].ToString();
string t2 = dr[1].ToString();
string dd1 = dr[2].ToString();
string t3 = dr[3].ToString();
string sql = "insert into table1 values('" + t1 + "','" + t2 + "','" + dd1 + "','" + t3 + "')";
SqlConnection cn = new SqlConnection("conn");
SqlCommand cmd = new SqlCommand(sql, cn);
cn.Open();
cmd.ExecuteNonQuery();
cn.Close();
}