A mobile sealing structure for a spirulina cultivation greenhouse comprises an arched top, two lateral surfaces and a front side, and is characterized in that the lower parts of the front and the back sides of the arched top are connected to form a rectangular double-layer structure through supporting rods and movable rods on two sides; fixed window screen cloth is fixed between the supporting rods and the movable rods; high-light-transmittance plastic cloth capable of moving up and down can be reeled on the movable rods; an inlet and outlet door is arranged at the lower part of the front side of the rectangular double-layer structure; and the arched top, the two lateral surfaces and the front side of the greenhouse are hermetically covered with high-light-transmittance plastic cloth. The utility model solves the conflict of sealing and ventilation; the greenhouse can be kept airtight so as to keep an appropriate and relatively constant thermal condition, so that mosquitoes, flies and other insects are prevented from entering, and influence of external adverse weather such as rain and snow can be avoided; and in addition, ventilation can be carried out to ensure that gas exchanges fully, so that sufficient silicon sources required by growth of spirulina can be supplied to be resolved in culture solution, and the structure is applicable to various forms of spirulina cultivations.