I think my first choice is master cylinder like Jcyuhn said. He poined out for the same problem for someone with exact locking and the problem was solved. Also, my parking brake is pretty loose and take 5-6 clicks to barely hold. And the symptom always automatic solved after 30-60 minutes may suggest master sylinder will release the pressure of the fluid in time. But parking brake is total mechanic system, and it unlikely auto release every time. And I will definitely change the pad (though I hate the dust thing) and check rotors and cater. And all your posts gave me valuable respect to consider. Thanks again.
Another thing is where to find a good deal on master cylinder and rebuit cylinder is reliable? Or repair kit is workable? Is there anyone have any comment on this?