先说实在的：最终解决办法是实现IDocHostUIHandler接口，在GetHostInfo方法里解决，但“实现接口”意味着QueryInterface、AddRef、Release三个方法必须实现，所以相关代码是：
class CMyWebBrowser : public IDocHostUIHandler
{
public:
    CMyWebBrowser() { m_cRef = 0; }
    virtual ~CMyWebBrowser() {}

    LONG                m_cRef;

private:
    HRESULT STDMETHODCALLTYPE QueryInterface(REFIID riid, void **ppvObject)
    {
        HRESULT result = S_OK;

        if (IsBadWritePtr(ppvObject, sizeof(LPVOID))) 
            result = E_INVALIDARG;  

        if (result == S_OK)
        {
            *ppvObject = NULL; 

            if ( IsEqualIID( riid, IID_IUnknown ) )
                *ppvObject = this;
            //             else if ( IsEqualIID( riid, IID_IOleClientSite ) )
            //                 *ppvObject = (IOleClientSite *) this;
            else if ( IsEqualIID( riid, IID_IDocHostUIHandler ) )
                *ppvObject = (IDocHostUIHandler *) this;
            else
                result = E_NOINTERFACE;
        }

        if (result == S_OK)
            this->AddRef(); 

        return result; 
    }

    ULONG STDMETHODCALLTYPE AddRef(){
        InterlockedIncrement(&m_cRef); 
        return m_cRef;
    }

    ULONG STDMETHODCALLTYPE Release() {
        ULONG ulRefCount = InterlockedDecrement(&m_cRef);

        return ulRefCount; 
    }

    HRESULT STDMETHODCALLTYPE EnableModeless(BOOL fEnable) { return S_OK; }

    HRESULT STDMETHODCALLTYPE FilterDataObject(IDataObject *pDO,IDataObject **ppDORet){return S_OK;}

    HRESULT STDMETHODCALLTYPE GetDropTarget(IDropTarget *pDropTarget, IDropTarget **ppDropTarget){return S_OK;}

    HRESULT STDMETHODCALLTYPE GetExternal(IDispatch **ppDispatch){return S_OK;}

    HRESULT STDMETHODCALLTYPE GetOptionKeyPath(LPOLESTR *pchKey,DWORD dw){return S_OK;}

    STDMETHOD(GetHostInfo)(DOCHOSTUIINFO *pInfo) {
        pInfo->cbSize = sizeof(DOCHOSTUIINFO);
        pInfo->dwFlags |= DOCHOSTUIFLAG_NO3DBORDER;
        pInfo->dwDoubleClick = DOCHOSTUIDBLCLK_DEFAULT;
        pInfo->pchHostCss = 0;
        pInfo->pchHostNS = 0;

        return S_OK;
    }

    HRESULT STDMETHODCALLTYPE HideUI(VOID){return S_OK;}

    HRESULT STDMETHODCALLTYPE OnDocWindowActivate(BOOL fActivate){return S_OK;}

    HRESULT STDMETHODCALLTYPE OnFrameWindowActivate(BOOL fActivate){return S_OK;}

    HRESULT STDMETHODCALLTYPE ResizeBorder(LPCRECT prcBorder,IOleInPlaceUIWindow *pUIWindow,BOOL fFrameWindow){return S_OK;}

    HRESULT STDMETHODCALLTYPE ShowContextMenu(DWORD dwID, POINT *ppt, IUnknown *pcmdtReserved,IDispatch *pdispReserved){return S_OK;}

    HRESULT STDMETHODCALLTYPE ShowUI(DWORD dwID,
        IOleInPlaceActiveObject *pActiveObject,
        IOleCommandTarget *pCommandTarget,
        IOleInPlaceFrame *pFrame,
        IOleInPlaceUIWindow *pDoc
        ){return S_OK;}

    HRESULT STDMETHODCALLTYPE TranslateAccelerator(LPMSG lpMsg,
        const GUID *pguidCmdGroup,
        DWORD nCmdID
        )
    {return S_OK;}

    HRESULT STDMETHODCALLTYPE TranslateUrl(DWORD dwTranslate,
        OLECHAR *pchURLIn,
        OLECHAR **ppchURLOut
        )
    {return S_OK;}

    HRESULT STDMETHODCALLTYPE UpdateUI(VOID) {return S_OK;}
};

1.要写的更通用一点，就是上述类就这么些内容，然后WEBBrowser从这个类继承。

2.除了实现这个接口外，别忘了SetUIHandler，这个不难查到，这里就不写了。

牢骚一下：项目中用到WEBBrowser，由于项目组中只有我一个人做过WEB，所以这玩意一直是我维护，最近由于我给里面的Html加了DocType，导致WEBBrowser出现了3D边框，不管是css的border:0还是body的leftmargin和topmargin，都不管用，查了很多资料（主要是google外国人的），都说实现IDocHostUIHandler接口，在GetHostInfo方法里能干掉3D边框，但我按照网上做的，结果要么报错，要么GetHostInfo不走，郁闷了我，折腾了两天，最后几乎不懂COM的我还是觉得QueryInterface等3个方法要实现，结果去查，果然如此，实现之后，搞定~~~

C++（MFC）中WebBrowser去除3D边框的方法（实现IDocHostUIHandler接口）,布布扣,bubuko.com

C++（MFC）中WebBrowser去除3D边框的方法（实现IDocHostUIHandler接口）