Thank you so much for the help.
It is a pity that I can put the picture in. 
If I am right, the "gold finger" of the graphic card (PCI exX16) is something like this
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Is it right that I only the Female end of the extension cable to the blue part, leaving the red part empty to the air?
I want to make sure about that. It is the first time that I used the extension cable and I am a litter afraid that I may burn my motherboard into ashes.
Thanks again for any help.