Fuente: WIPO "hemp" The invention provides a hemp yarn swelling method which comprises the following steps: step 1, putting hemp yarn into a closed container, then putting liquid ammonia into the closed container, and enabling the liquid ammonia to react with the hemp yarn; 2, taking out the reacted linen yarn, and putting the linen yarn into a high-temperature steam box for reacting to enable ammonia gas to flow out; 3, the dried linen yarn is taken out and put into a washing device to be washed and eliminate residual liquid ammonia, the linen yarn is dried in the high-temperature steam box at the high temperature, ammonia gas flows out, the internal stress of fibers is eliminated, and steam in the high-temperature steam box can keep the swelling degree of the fibers and reduce the swelling and retraction rate.