Han dynasty stabilized grain prices by trading against the market

China's grain markets swung between two extremes every few years: bumper harvests crashed prices so low that farmers couldn't cover their costs, while lean years drove prices so high that ordinary people couldn't afford to eat. Officials had already tried fixing prices by decree, but a legally mandated price that ignored actual supply and demand was either unenforceable, ignored by merchants who traded around it, or actively made shortages worse by removing any incentive to bring more grain to market when it was needed most.

Simply stockpiling grain for emergency famine relief, the traditional response, didn't address the underlying price volatility hurting farmers in good years just as much as it hurt consumers in bad ones. What was needed was a mechanism that could dampen the price swing itself, in both directions, without any legal price ever being declared.

During the reign of Emperor Xuan of Han (r. 74–49 BCE), the official Geng Shouchang extended an existing price-stabilization approach into a formal 'ever-normal granary' (changpingcang) system: the state itself became a standing buyer of grain at harvest, purchasing large quantities — an initial purchase on the order of 400,000 hu is recorded — to support prices when supply was abundant, then a standing seller from its own stockpiles during lean months to hold prices down, trading on both sides of the market rather than declaring any price by decree.

The state became a standing buyer at harvest and seller in lean months, trading against the market to smooth prices without decreeing them.

Buying at harvest supports prices, protecting farmers' incomes.

Selling in lean months caps prices, keeping food affordable.

The state's large stockpiles give it enough weight to move the market.

No legal price is declared, so merchants still have incentives to trade.

To tame price volatility, take a standing position on both sides of the market—buy low, sell high—rather than fixing prices, which distorts supply and is unenforceable.

The system spread and was refined across subsequent dynasties, reaching its largest scale under the Qing, when a nationwide network of ever-normal granaries held on the order of 2.2 to 3.3 million tonnes of grain and is credited with saving over 100 million lives through famine relief drawn from the same stockpiles used for routine price stabilization.