How can i get host application handle in dll project with Delphi without passing handle parameter

You are looking for top-level windows in your process. Find them like so:

1. Call GetCurrentProcessId to obtain your process ID.
2. Call EnumWindows to enumerate all top level windows.
3. In the enumeration callback, for each top level window, call GetWindowThreadProcessId to obtain the process ID that owns the window. Any that match the process ID found in step 1 are from your process.

The problem that you face is that step 3 might identify multiple such windows. You can call GetWindow passing GW_OWNER to obtain the owner of the window and use that to trim down the field of candidates. What you perceive as being the main window is likely to have no owner, but the other top level windows may well be owned. Even this cannot be guaranteed to trim the field down to a single candidate and you very likely will need to come up with some additional logic.