连二亚硫酸钠（sodium dithionite），又称低亚硫酸钠、保险粉。分子式Na₂S₂O₄，分子量174.11。是一种强还原剂。

外观为白色砂状结晶物或淡黄色粉末，略带有硫的味道，熔点52-55℃（分解），沸点130℃（分解）。密度为2.19，引燃温度为130℃。可溶于水，不溶于乙醇。

连二亚硫酸钠可以通过以下反应制备：

①SO2+2NaOH===Na2SO3+H2O

②H2SO3+Na2CO3===Na2SO3+CO2↑+H2O

③2NaHSO3==△==Na2SO3+H2O+SO2↑

Sodium dithionite (also known as sodium hydrosulfite) is a white crystalline powder with a weak sulfurous odor. It is the sodium salt of dithionous acid. Although it is stable under most conditions, it will decompose in hot water and in acid solutions. It can be obtained from sodium bisulfite by the following reaction: