Paraquat poisoning can cause delayed pulmonary fibrosis within 1-2 weeks after the acute stage, and pulmonary fibrosis can be life-threatening, because pulmonary fibrosis caused by paraquat poisoning can lead to respiratory difficulties, or even respiratory failure, which is life-threatening. Paraquat poisoning is usually a gastrointestinal reaction, but after 1-2 weeks due to the toxin of paraquat can cause the body to produce a large number of free radicals, free radicals can destroy tissue cells, especially in the lung tissue can be aggregated, so the lungs caused by the damage is relatively large. After the alveolar cells are damaged, fibrosis will replace them, and the respiratory function of the lungs will be seriously affected after fibrosis occurs in the whole lung.