A composition for controlling ambient humidity within 45%˜55%. The composition includes at least one organic acid salt, at least one of polyol and water. The organic acid salt includes at least one of sodium lactate, potassium lactate and sodium formate. The count of carbon in the polyol is not greater than 5. The weight percentage of the organic acid salt in the composition is 30.6%-58.8%. The weight percentage of the polyol in the composition is 9.3%-26.7%. The composition can control the ambient humidity within 45%˜55% without the need to pre-adjust the objective space. The composition has a large capacity of moisture absorption and desorption, and can quickly achieve the desired humidity in the objective environment.