The invention relates to a water level control method for a flush toilet water tank and a water saving toilet. Under the default condition, the water level in a water tank is at a low level, at that time, when the flushing is started, only a little water stored in the water tank is used for flushing the toilet. When a toilet seat is put down, the toilet carries out supplement water filling according to an original set program; and when the water level rises to a high level, the toilet stops filling water to the water tank. The toilet automatically fills water into the water tank after flushing of each time, and when the water level in the water tank reaches the low level from the zero level, the toilet pauses to fill water into the water tank. When the water tank of the toilet is in the low water level for a long time, only a small part of parts are soaked in the water, and the water pressure at the bottom of the water tank is smaller relative to that of the existing water tank. The parts of the water tank in the invention have long service life, avoid the water waste caused by the faulty operation of users, and can judge flush amount according to the type of the used toilet.