Experimental studies were carried out on the basic light demand for brood-bud germination of submerged plant Vallisneria spiralis L., Hydrilla verticillata Royle, Ceratophyllum demersum and Potamogeton crisptts L. Intense light stimulation could break dormancy of brood-buds of P. crispus and lead to germination in the early summer In natural water body, summer dormancy of P. crispus brood-buds may be caused by low light intensity in the bottom. Light was not indispensable for brood-bud germination in the other three plant, but low relative radiation intensity (less than 5%) would cause albino young shoot which could not carry out normal photosynthesis. Thus, light condition at lake bottom in brood-bud germinating season was the key environmental factor for submerged plant to survive.