Ascariasis is the most common intestinal parasitic disease. The source of infection is patients with ascariasis and infected people. A large number of eggs are excreted with the patient's feces, contaminating vegetables and soil. Under suitable temperature and humidity, they develop into mature eggs in about 2 weeks. The mature eggs go to the stomach through the mouth, and most of them are killed by gastric acid. A few enter the small intestine to hatch and develop into larvae. The larvae drill into the intestinal mucosa, enter the portal vein, liver, and inferior vena cava through the lymphatic vessels or microvessels to reach the lungs; after molting in the lungs, they form larvae of about 1 mm. The larvae pass through the microvessels, rise to the pharynx through the alveoli, bronchi, and trachea, and then are swallowed into the stomach, which constitutes ascariasis. Ascariae develop into adults after reaching the small intestine. It takes about 75 days from swallowing eggs to adult maturity, and the survival period in the small intestine is about 1-2 years.