Method 1：
Link：Debugging COM and ActiveX
Link：How to: Debug an ActiveX Control
Step1：Code test html.
<HTML> <HEAD> <TITLE>Test ActiveX</TITLE> </HEAD> <BODY> <OBJECT ID="MyActiveX" WIDTH=800 HEIGHT=600 CLASSID="CLSID:5228A02F-8FBD-424C-B457-EEBD4E748504"> <PARAM NAME="_Version" VALUE="65536"> <PARAM NAME="_ExtentX" VALUE="4657"> <PARAM NAME="_ExtentY" VALUE="4075"> <PARAM NAME="_StockProps" VALUE="0"> </OBJECT> </BODY> </HTML>
Step2：Set debug option in VS2010.
Right click the project and select "Properties" tab. Then select Debugging item in the Properties Pages and configure "Command" and "CommandArgs" arguments.
command: C:/Program Files/Internet Explorer/iexplore.exe (Local IE path)
command arguments: C:/test.htm (test.html file path)
Step3: Register ActiveX control using full path.
If not, there will be an error：The sepcified module could not be found.
Step4: Sep break point in VS2010 where the implement code you want to debug. Then press F5 to run the program.
Note：IE8 is multi-thread by default, doesn't support ActiveX debug. So, you must modify the registry as following:
[HKEY_CURRENT_USER\Software\Microsoft\Internet Explorer\Main]
"TabProcGrowth"=dword:00000000