lyjqhjcplusplus wrote: Another 3rd party, provided a implicit linking library, tool.lib. so I modified code, regenerated EXT.DLL as below: 1) Link the tool.lib by modify the Project Configuration - Linker Input 2) Include the header file tool.h 3) Add one line in my EXT.DLL source code, which call the funtion exported in tool.lib. This is how I interpret what you've said so far: You are implicitly linking the "Tool" library with your "Ext" library, but it seems like you are explicitly linking your "Ext" library to your application. When you're trying to load your "Ext.dll" with ::LoadLibrary(), it fails to load since the "Tool.dll" cannot be found. Forget about the Tool.lib file, it's not used after the "Ext.dll" has been successfully built. You have to read the documentation I linked to earlier, otherwise it serves no point in trying to help you. If you would have bothered to read it, you should have solved this by now. "It's supposed to be hard, otherwise anybody could do it!" - selfquote "High speed never compensates for wrong direction!" - unknown