The invention discloses a water-through quenching cooling device and method capable of realizing rapid cooling through slit water injection. As for the water-through quenching cooling device capable of realizing rapid cooling through slit water injection, openings of water injection slits are arranged along the axial direction of a quenching cooling object, the water injection slits are arranged on the circumference of the quenching cooling object, and the adjustment on the cooling strength and cooling uniformity of the quenching cooling object can be realized by adjusting the water injectionamount, water injection pressure and the opened amount of the water injection slits. Compared with the traditional device, the water quenching cooling device can provide higher cooling strength, has no special requirements on water quality and filter granularity, and can reach the cooling strength required by martensite, bainite or a mixture of the martensite and bainite for steel bars, bars, profiled bars and steel rails. Furthermore, the device in the invention is large in cooling strength application range, and can be widely used on the steel bars, bars, profiled bars or steel rails of martensite, bainite or a mixture of the martensite and bainite.