找到解决了, 弄了一周了.
QDesignerDynamicPropertySheetExtension* propertySheet = 0;
QExtensionManager* manager = formEditor->extensionManager();
propertySheet = qt_extension<QDesignerDynamicPropertySheetExtension*>(
manager, widget);
int pi = propertySheet->addDynamicProperty("testProperty", "test Value");