the `Flash Player` occupy CPU is very high after I open a Flash page
The red color means that the program is no longer responding to the operating system. This is often because the program has crashed, but it might also be that it is because the program is slowed down by waiting for the disk, memory allocation or similar. If that is the case, the program will be listed in black again, when it does respond.

In your case it seems reasonable to think that the Flash Player has indeed crashed, as it is not supposed to be doing a lot, if you haven't got any Flash pages open in your browser.

You can click on the Flash Player item in Activity Monitor and press the circled-cross icon in the toolbar, which will force kill the program - releasing the resources for other programs to use.

If you haven't updated Flash Player and/or your browser recently, I would suggest updating to the latest version which could potentially fix the problem.