Doctor, my mouth always bleed when i brush my teeth, this situation have a long time, and appear cyst sometimes. what's problems in my mouth?

Flossing: Without seeing your mouth it could be your gums are inflamed and need to get in shape floss once a day 10x's/tooth and rinse with Peridex (chlorhexidine gluconate) might get them healthy. Or there could be a hormone issue. I do not understand the cyst part.

Gum disease: Any bleeding is the sign of infection or inflammation. It usually doesn't hurt, so many people disregard it. The incidence of a cyst would confirm the presence of infection. You can try and brush and floss perfectly, but there is some underlying disease that will have to be treated by a dentist or hygienist.

Periodontal disease?: Bleeding is nature's way of telling you that something is wrong. The most common cause of bleeding gums is some form of periodontal (gum) disease. The fact that you have had it a long time is of more concern, as the longer you postpone treatment, the more money, time & treatment you will need to correct the problem. See your dentist asap for a diagnosis and treatment. It won't go away on its own!