Diquat is a non-selective contact herbicide with slight conductivity. After being absorbed by green plants, the electron transfer of photosynthesis is inhibited. Under light induction, the reductive bipyridine compounds are oxidized quickly in the presence of oxygen to form active hydrogen peroxide. The accumulation of this substance destroys the plant cell membrane, and the drug-treated parts will be withered . It can also be used as seed plant desiccant and dehydrating agent for potatoes, cotton, soybeans, maize, sorghum, flax, sunflower and other crops; when dealing with mature crops, the remaining green parts and weeds quickly withered, which can make the harvest earlire and cut the loss. It can also be used as an inhibitor of inflorescence formation of sugarcane. Because it can't penetrate the mature bark, it can hardly destroy the underground polar stem. It can be used to accelerate crop withering with dosage of 3-6g active ingredient/100m2. For weeding in farmland, the amount of no-tillage weeding in summer maize was 4.5-6g/100m2, and that in orchard was 6-9/100m2. Direct spraying of young saplings should not be avoided, because the green part of crops will cause phytotoxicity.