This invention discloses a ventilation system for an MRI system, including: a hydrodynamic rotating device, a primary coolant water pipe, a secondary coolant water pipe, a fan and air outlet; the water outlet of the primary coolant water pipe is connected to the water inlet of the hydrodynamic rotating device, while the water inlet of the secondary coolant water pipe is connected to the water outlet of the hydrodynamic rotating device; with the impetus provided by the coolant water from the primary coolant water pipe, the hydrodynamic rotating device drives the fan near the air outlet to rotate, discharging the coolant water into the secondary coolant water pipe. Furthermore, the invention discloses a ventilation method for an MRI system. Ventilation efficiency is improved significantly with the system and method provided by this invention.