Function HexToStr(S: String): String;

Var

  Stream: TMemoryStream;

  Value: TStringStream;

  Pos: Integer;

Begin

  Result := '';

  If Length(S) > 0 Then

  Begin

    Stream := TMemoryStream.Create;

    Value := TStringStream.Create('');

    Try

      Pos := Stream.Position;

      Stream.SetSize(Stream.Size + Length(S) Div 2);

      HexToBin(PChar(S), PChar(Integer(Stream.Memory) + Stream.Position), Length(S) Div 2);

      Stream.Position := Pos;

      Value.CopyFrom(Stream, Length(S) Div 2);

      Result := Value.DataString;

    Finally

      Stream.Free;

      Value.Free;

    End;

  End;

End;

Function StrToHex(S: String): String;

Var

  Stream: TMemoryStream;

  Value: TStringStream;

Begin

  If Length(S) > 0 Then

  Begin

    Value := TStringStream.Create(S);

    Try

      SetLength(Result, (Value.Size - Value.Position) * 2);

      If Length(Result) > 0 Then

      Begin

        Stream := TMemoryStream.Create;

        Try

          Stream.CopyFrom(Value, Value.Size - Value.Position);

          Stream.Position := 0;

          BinToHex(PChar(Integer(Stream.Memory) + Stream.Position), PChar(Result), Stream.Size - Stream.Position);

        Finally

          Stream.Free;

        End;

      End;

    Finally

      Value.Free;

    End;

  End;

End;

来源：https://bbs.csdn.net/topics/390876064