Disclosed is a plate-and-frame filter press capable of efficient and constant-speed discharge for processing contaminated bottom sediment in rivers, lakes and streams. The plate-and-frame filter press comprises a machine frame (1), a filter plate group (2), a pressing mechanism (3), a rotary discharging mechanism (4) and a power device (5). The filter plate group (2) comprises multiple filter plates (21) disposed in parallel. The rotary discharging mechanism (4) comprises a guide rail (41) and plate-pulling trolleys (42). The multiple plate-pulling trolleys (42) are driven by the power device (5), and perform unidirectional constant-speed movement along the guide rail (41). Each of the plate-pulling trolleys (42) respectively pulls one filter plate (21) of the filter plate group (2) during a movement process.