The invention discloses a fire water monitor head for performing direct current spray conversion by adopting hydraulic drive, which comprises a nozzle shell, a nozzle, a nozzle core, a nozzle core rack, a cylinder body, a pipe joint, a water delivery hose, a three-position four-way pure water electromagnetic directional valve, a seal ring and the like. The fire water monitor head uses the most common pressure water in a fire-extinguishing scene as a power source, and is operated through conductive driving valve cores of electromagnets at the left end and the right end of the three-position four-way pure water electromagnetic directional valve to pressurize a left water pressure cavity and a right water pressure chamber of the nozzle respectively so that the nozzle slides back and forth to realize the automatic smooth conversion between direct current injection and spray injection for the fire water monitor head. By adopting the hydraulic drive directly, the fire water monitor head overcomes the defects of complex mechanism and large volume when a hydraulic control telescopic cylinder or an electric control driving mechanism is adopted to realize the direct current spray conversion at present. The fire water monitor head namely a conversion device has a simple and compact structure, is convenient to operate, and is particularly suitable for the occasions in need of achieving various functions such as fire distinguishing, cooling, diluting, protecting and the like during fire fighting.