Variable diaphragm and control method thereof

A variable diaphragm is provided. The variable diaphragm includes: first and second substrates opposite to each other; a light detector on a side of the first substrate distal to the second substrate, and configured to detect an intensity of incident light and generate a first signal; an electrowetting microfluid medium layer between the first and second substrates, and including transparent and opaque fluid mediums immiscible with each other, wherein an aperture of the variable diaphragm is formed by the transparent fluid medium, and one of the transparent and opaque fluid mediums is conductive; and a driving electrode between the first and second substrates, and configured to receive a driving voltage corresponding to the first signal and for driving the electrowetting microfluid medium layer, so as to change an area of an orthographic projection of the opaque fluid medium fluid medium on the second substrate, thereby changing a diameter of the aperture.