The utility model provides a boiler deaerator, comprising a deaerator body, wherein a water feeding pipe and a water discharging pipe are respectively arranged at the upper part and the lower part of the deaerator body; an oxygen discharging pipe with a check valve and a drain pipe are arranged at the top part and the bottom part of the deaerator respectively; a diffusion pipe is further arranged at the top part of the deaerator and an instrument is further arranged at the top part of the deaerator. With the adoption of the technical scheme, the boiler deaerator has the following advantages that: a set of diffusion pipe is additionally arranged at the top part of the deaerator; when the water pressure in the deaerator body is higher than a saturated pressure, a valve on the diffusion pipe is opened to reduce the pressure, so that the pressure and the temperature in the deaerator body are just at saturated conditions and oxygen is completely removed. Therefore, a subsequent water pump cavitation phenomenon is avoided.