The utility model discloses a filter, which comprises a box body, a roller, a motor, a spraying assembly and a collecting groove. The spraying assembly arranged above the roller comprises a spraying tube and a plurality of nozzles on the spraying tube. The spraying tube is communicated with an output end of a water pump outside the box body of the filter through a pipeline. One end of the collecting groove suspended and fixed in the box body extends into the roller while the other end is communicated with a drain outlet on the box body. During automatic cleaning, the motor drives the roller to rotate and the spraying assembly sprays high pressure water to a filter screen with residue in periphery of the roller. The high pressure water passes through the filter screen and sewage flows into the collecting groove and discharged out of the box body through the drain outlet. The filter has high degree of automation and high backwashing and water-saving efficiency. The roller is high in concentricity and stable in operation. The filter can realize highly sensitive liquid level control with stable and reliable performance and control of the rotate speed of the roller. The power system of the spraying assembly resists seawater corrosion and has long service life. The filter has good solid-liquid separation capacity and high efficiency with the solid recycling rate greater than 90%.