The invention relates to a structure improvement and a making method of a humidity sensor on the basis of polyimide and filler corrosion. The structure improvement is characterized in that after filling materials in a polyimide layer between electrode plates, carrying out corrosion and making a porous thin film, and after photoetching, a, a single cavity is made along the direction of the electrode plates; b, a plurality of cavities are made along the direction of the electrode plates; c, a plurality of cavities are made in the direction vertical to the electrode plates; d, a plurality of independent cavities are made in the porous polyimide thin film between the electrode plates; or e, a plurality of independent polyimide blocks are reserved in the porous polyimide thin film between the electrode plates. The making method comprises the following steps of: firstly, sputtering a metal layer serving as a seed layer on a silicon wafer; then electroplating capacitor electrode plates; coating a polyimide adhesive serving as a dielectric material of a capacitor; filling optical fibers, glass powder or metal granular materials in the polyimide; corroding the filling materials in the polyimide to obtain the porous polyimide thin film; and finally, forming the cavities by adopting an photoetching method, so that the contact area of the porous thin film and the air is increased and the sensitivity of the sensor is improved.