Abstract: Abstract: Based on the requirements of harvesting methods and harvesting for sugar beet at home and abroad, a method of smashing leaf and top cutting thickness was proposed, and a kind of fixed thickness top cutter was designed. The machine can complete the smashing leaf, cleaning leaf and cutting top of sugar beet at one time, which is composed of traction frame, hydraulic cylinder, transmission system, smashing leaf mechanism, cleaning leaf mechanism, position following mechanism, pressure adjustment mechanism, equal thickness cutting mechanism, walking mechanism, and so on. Among them, the smashing leaf mechanism, cleaning leaf mechanism, position following mechanism and equal thickness cutting mechanism are the key components. Through theoretical analysis, the transmission configuration relationships were obtained, and the structural parameters of the key components were determined. The smashing leaf mechanism is composed of 2 rows of rotary knife, and installation density of knife was 25 pieces/m. The cleaning leaf mechanism is composed of 4 rows of rubber strips, and installation density of rubber strips was 26 pieces/m. And the misalignment arrangement of the spacer and the rotary knife or the spacer and the rubber strip was designed for smashing or cleaning leaf. The structural parameters of the S-shaped rotary knife and the rectangle rubber strip were determined to meet the strength requirements of the parts, the cleaning effect and the lower damage of the beet. The blade angle ε1 was 26°, the slip angle β1 was 15°, the bend angle φ was 120°, the rotary knife width B1 was 40 mm, the length L3 was 170 mm; the rubber strip width B2 was 40 mm, the thickness b was 5 mm, the length L4 was 260 mm. Through the kinematics and mechanical analysis of the following cutters, important working parts of the side rod, following board and the cutter were designed, which affect the quality of the cutting beet top. And the important structural parameters of the position following mechanism were determined, which affect the work quality of the cutting device. Combined with the working process of the sugar beet cutter, the installation position and structural parameters of the cutter were determined. The structural parameters included: the connecting rod L6 of 320 mm, the following board height H3 of 125 mm, the following board bending angle α2 of 35°, the following board installation angle β2 of 55°, and the cutting angle ε2 of 25°, cutting rake angle δ of the knife of 0°, and the cutter width B4 of 50 mm. The field test results show that the top-cutting pass rate is 93.6%, and the multi-cutting rate is 2.1%, which meets the index requirements of beet top harvesting. This research can provide basis for the development of sugar beet harvester.