Sewage treatment device and control method thereof

The invention discloses a sewage treatment device and a control method thereof, and belongs to the technical field of sewage treatment. The device comprises a grating flocculation tank (1) and a biological treatment tank (2) which are connected in sequence; an outlet of the biological treatment tank (2) is connected with the lower part of a photocatalysis tank (4) through a first pump (3), and the first pump (3) conveys sewage from the biological treatment tank (2) to the photocatalysis tank (4); the top of the photocatalytic tank (4) is communicated with a second pump (5), an inlet of the second pump (5) is positioned at the upper part of the photocatalytic pool (4), an outlet of the second pump (5) is connected with a first water quality detection device (11), and an outlet of the first water quality detection device (11) is connected with a first water outlet valve (16); and the device further comprises a third pump (6) which is used for conveying the sewage of the photocatalysis tank (4) to a membrane tre