Data table taking too much time to load 50000 records.suggest its solution.

Try it this way:

SqlConnection  conn      = null;
SqlCommand     cmd       = null;
SqlDataAdapter adapter   = null;
DataSet        dataset   = null;
DataTable      dataTable = null;

try
{
    using (conn = new SqlConnection("connection string"))
    {
        conn.Open();
        using (cmd = new SqlCommand("sp_web_reports", conn) { CommandType = CommandType.StoredProcedure })
        {
            cmd.Parameters.AddWithValue("@mode",      50);
            cmd.Parameters.AddWithValue("@From_Date", Convert.ToDateTime(txt_from_date.Text));
            cmd.Parameters.AddWithValue("@TO_Date",   Convert.ToDateTime(txt_to_date.Text));
            cmd.Parameters.AddWithValue("@GroupCode", drp_vehicle_group.SelectedValue);
            using (adapter = new SqlDataAdapter(cmd))
            {
                dataset = new DataSet();
                adapter.Fill(dataset);
                dataTable = dataset.Tables[0];
            }
        }
    }
}
catch (Exception ex)
{
    // handle the exception
}

// if you get here without an exception, you can work with your dataTable object.

The using statement has the benefit of cleaning up the adapter, command, and connection objects without writing code to specifically handle that. Furthermore, you should wrap ALL ADO code with try/catch blocks and handle the exceptions appropriately. Defining the various objects before the first using statement allows you to examine them in the debugger in the event an exception is raised.

If you want to export to Excel, all you have to do is call dataTable.WriteXML("filename"), and Excel 2007+ can read it.

As far as I can see:
1) you forgot to tell how long is 'long'.
2) The way your stored procedure join the 2 tables have impact on execution time, but you didn't showed that procedure.
3) the database structure and indexes matters too, but it is mystery too.

The bad news: There is no secret super fast magic command that will give you instant result of 50k records.
Only the correct database design and correct query will minimize the run time, every mistake will dramatically downgrade performance.

Have you reviewed your indexing on the tables in question?
Does your SQL Statement have a "select *"?

c# - DataTable Load very slow - Stack Overflow[^]
c# - SQL Query that runs fine in SSMS runs very slow in ASP.NET - Stack Overflow[^]

The DataTable is inherently slow to begin with. There's not much you can do to make that go faster.

The problem may be because you're query isn't optimized. We don't know because we can't see it in what you posted.

But, you also said the 50,000 records you're dealing with could be larger. Using a DataTable imposes a limit on the number of records you can deal with. You're trying to load the entire set of records into memory at the same time because of the limitation on RAM in the machine. It's a really bad idea to load that number of records into memory.

Since you're exporting the data to Excel, don't use a DataTable. Use a DataReader instead. that will only load one record at a time into memory. Load the record, export it to your Excel sheet, load the next one and repeat until done. You don't have any memory limit issues to deal with.

You should be using Excel's "Data" feature to import directly into Excel from SQL Server.

Too many intermediate steps otherwise.

Or export from SQL Server as CSV; open in Excel.

etc.