The invention relates to a thickener and a method for applying the same in liquid-solid separation. The thickener comprises a tank (11), a motor (9), a reducer (10), an axially rotating hollow shaft (4), a feed tube and at least two filter disks (5) with central holes; the motor and the reducer are directly connected and drive the hollow shaft via a coupling (12); the feed tube is arranged insidethe tank and is parallel with the hollow shaft; the filter disks (5) are vertically fixed on the hollow shaft, a feed distribution tube (3) is arranged between the neighboring filter disks, and scrapers (6) are fixed in parallel on the feed distribution tube. The invention also relates to the method for applying the thickener in liquid-solid separation, concentrated catalyst particles return to areaction system via a concentrated solution discharge outlet (7), filtrate is discharged via a filtrate discharge outlet (8), and the content of solid in the filtrate is less than 0.2ppm. The thickener has the advantages of low fabrication cost, high transmission efficiency, easy control, easy and reliable operation and high safety.