A sewage treatment system, comprising a pre-treatment system (1), an anoxic system (2), a photoreaction system (3), an algae-bacteria separation system (4), and a film separation system (5). The pre-treatment system (1) comprises a grille (11) and a sand sedimentation tank (12), and is communicated with the anoxic system (2). The anoxic system (2) is provided with a first stirring device (21), and is communicated with the photoreaction system (3). The photoreaction system (3) is provided with a second stirring device (31), and is communicated with the algae-bacteria separation system (4). The algae-bacteria separation system (4) is communicated with the anoxic system (2) and the film separation system (5). A second outlet of the algae-bacteria separation system (4) is used for discharging a part of algae-bacteria symbiont. The film separation system (5) is communicated with the anoxic system (2). A second outlet of the film separation system (5) is used for discharging a part of microalgae, and a third outlet of the film separation system (5) is used for discharging the treated sewage. The anoxic system, the photoreaction system, and the algae-bacteria separation system all comprise the algae-bacteria symbiont and the suspending microalgae. Also disclosed is a sewage treatment method.