The origin of Lu Yin: In the Ming Dynasty, it was stipulated that anyone who was far away from his place of residence should issue an official document, such as a letter of introduction and a pass, which was called "Lu Yin". If there is no "Lu Yin" or it does not meet it, they will be punished according to the law. "Lu Yin" is actually a proof of leaving home.
In the Ming Dynasty, Li Jia system was called Baojia system. "Hundreds of households have one Li, ten households have more food stalls, and more than 100 households have ten Jia. Jia Fan has ten people. The old-age service is one person, the first person. " The law of the Ming dynasty stipulated that "farmers should not go out for a mile, but go in at dusk to know each other's way of working and rest".