SqlBulkCopy

using (SqlConnection Bulkconn = new SqlConnection(conn.ConnectionString))
{
    Bulkconn.Open();

    using (SqlBulkCopy sqlBC = new SqlBulkCopy(Bulkconn))
    {
        sqlBC.DestinationTableName = "dbo." + dt.TableName;

        foreach (DataColumn dc in dt.Columns)
        {
            sqlBC.ColumnMappings.Add(dc.ColumnName, dc.ColumnName);
        }

        sqlBC.WriteToServer(dt);
    }
}