In the first year of Gan Yuan (758), the salt law was changed at the beginning of the Fifth Qi Dynasty, saying, "Try your best to buy all the salt in the world, and pay an extra 100 yuan for it, that is, 110 yuan" (The Book of the New Tang Dynasty, Records of Foodstuffs IV). During Baoying period, Ada, as an envoy of salt and iron, further revised the salt law, set up prisons in salt-producing areas, urged salt households to produce on their own, and added salt tax to the salt price to sell to merchants, leaving it to merchants to transport and sell, so as to increase fiscal revenue. When Liu Yan was appointed as the salt and iron envoy, the income from salt benefit was only 400 thousand yuan, and by the end of Dali period, it had increased to more than 6 million yuan. Han Yu's On Changing Salt Law: "If the country has a monopoly on salt, it will only be monopolized by merchants and merchants and people, and all the people in the world will lose money at the expense of officials" (Changli Collection, Volume 40).