The utility model provides an ultrasonic humidifier of adding water on outer exhaust passage, includes base, water tank, tank lid, atomizer, float sleeve, it can float and fan to gather, in the head of the supporting seat of base inserts the connection interface of water tank bottom, connects the lower extreme and supporting seat cooperation of interface, in the telescopic bottom entry atomizer seat of float and can dismantle the connection, gathers and can the float setting ends the position in the float sleeve and with the ring shape bedplate cooperation of float sleeve lower extreme, prop up supporting bench support cooperation in the upper end of tank lid embedding water tank and with the annular in the water tank, in the inner port that goes out the fog lid inserted the water tank, cover plate body ended the position with the upper end cooperation of water tank, cylindric play fog interface ends airtight position with the apron cooperation of tank lid, base and water tank are provided with scratches the hand chamber. Fan and main control board setting are in the base, when adding water, only need to go out the fog lid and can add water convenience with water tank top separation on realizing, when falling just, water directly goes out the fog lid and flows, can prevent that water from getting into the base, has protected fan and main control board.