A tyre pressure automatic controlling device is provided, which comprises a high pressure gasbag, a high pressure valve and a low pressure valve. The invention is characterized in that: the high pressure gasbag is a hollow round ring shape, which is fixed at the tyre, the high pressure gasbag and the high pressure valve are communicated by a pipeline, the low pressure valve and the tyre air chamber are communicated by pipeline, the high pressure valve and the low pressure valve are communicated with an air inlet. If the air pressure in the high pressure gasbag and the tyre air chamber is too large, which will discharge from the air discharging holes of the two valves, the pressure in the high pressure gasbag is too small, the pressure indicating arm contracts to warn the driver to charge, when the pressure in the tyre is smaller, the air of the high pressure gasbag will pass through the high pressure valve, low pressure valve and supply air to the tyre, which makes the pressure at the fixed value. The invention can effectively prevent the traffic accident caused by too large or too small tyre pressure, which can prolong the service life of the tyre and save burning oil consumption.