The invention discloses a device and method for extracting a volatile substance in water. The device comprises an aerating system, a condensation refluxing system and a capturing cold trap system. Theaerating system, the condensation refluxing system and the capturing cold trap system are successively connected to form a passage. The aerating system is used for feeding a helium gas into a water sample containing the volatile substance, and blowing out the volatile substance from a water phase to a gas phase. The condensation refluxing system is used for condensing and refluxing water vapor blown out along with the helium gas into the water sample, and enabling the blown-out volatile substance to enter the capturing cold trap system along with the helium gas. The capturing cold trap systemis internally provided with a condensation core which is used for gathering and capturing the blown-out volatile substance. The device is capable of effectively blowing out the volatile substance inthe water sample and gathering these volatile substances through a capturing cold trap. The device can be used for effectively evaluating a toxicity risk of the volatile substance in the water sample.