A solvent exchanger and a method is provided for: pressurizing a CTA slurry into a solvent exchanger for separation and obtaining a mother liquor, a bias flow mother liquor and a suspended matter A; washing the suspended matter A to obtain a primary filtrate, a bias flow primary filtrate and a suspended matter B; washing the suspended matter B to obtain a secondary filtrate, a bias flow secondary filtrate and a suspended matter C; washing the suspended matter C to obtain a tertiary filtrate, a bias flow tertiary filtrate and a suspended matter D; washing the suspended matter D to obtain a fourth filtrate, a bias flow fourth filtrate and a suspended matter E; washing the suspended matter E to obtain a fifth filtrate, a bias flow fifth filtrate and a filter cake; and after finished, back-flushing the filter cake and then pulping to obtain a slurry, and discharging.