A method for controlling a liquid treatment apparatus of the present disclosure includes: (i) providing the liquid treatment apparatus; (ii) treating a polluted liquid in a photocatalytic reaction tank by a photocatalytic reaction to produce a treated liquid; (iii) introducing a liquid mixture into a separation tank from the photocatalytic reaction tank through a feed passage by a circulation pump; (iv) introducing a filtrate to an outside of the separation tank through an extraction passage while filtering the liquid mixture introduced into the separation tank by a filtration membrane, and feeding the liquid mixture to the photocatalytic reaction tank through an overflow passage; and (v) making a flow rate of the liquid mixture measured by a liquid mixture flow meter higher than a flow rate of the filtrate measured by a filtrate flow meter by controlling the circulation pump by a controller.