The invention discloses a dynamic heating based flowing wet steam humidity sensor and a measuring method. The dynamic heating based flowing wet steam humidity sensor is characterized in that one side of an outer sleeve is internally sleeved with an inner sleeve; an insulated sealing layer is arranged between the inner sleeve and the outer sleeve; a wet steam temperature sensor is arranged on the inner wall of the other side of the outer sleeve; electrode pairs are circumferentially distributed; the wet steam temperature sensor, the electrodes, asuperheated steam temperature sensor and a superheated steam pressure sensor are sequentially arranged in the steam flowing direction; the superheated steam pressure sensor and the superheated steam temperature sensor are positioned within the same cross section which is perpendicular to the flowing direction; wet steam flowing into the humidity sensor is correspondingly heated to be superheated steam atdifferent temperature within two adjacent time intervals, and then the humidity is measured through the heat balance relation within the two adjacent time intervals. The method is applicable to online real-time measurement of the humidity of wet steam flowing in various narrow spaces.