The research on mechanized root cutting of garlic at home and abroad is still in the exploratory and experimental stage. Two key issues that remain unresolved in mechanized root cutting of garlic are low root cutting rate and high bulb bruise rate. In order to further study the operation mechanism and optimization design of garlic root floating cutting device, the theoretical study on the mechanical properties of root floating cutting process was carried out. The dynamics equations of bulb collision during root cutting were derived, and the relative velocity of bulb collision was the key motion parameter that affected the collision damage. The principle of root sliding cutting operation was analyzed, and the cause of root group cutting resistance was analyzed by establishing mechanical models of blade cutting resistance. The process of bulb collision, root group disturbance and fracture was analyzed by high-speed photography. The mathematical models were established to predict bruise rate and root cutting rate. The effects of various factors on bruise rate and root cutting rate were analyzed and the comprehensive optimization of various factors was carried out. The bruise rate was 2.78% and the root cutting rate was 93.17% under the optimal parameters of root floating cutting device with feed speed of 1m/s, rotational speed of the cutter of 2600r/min, cutter angle of 33°, and spiral grating pitch of 28mm. The research results can provide references for the research and mechanism design of garlic root cutting technique used in garlic combine harvester.