Lack of dissolved oxygen in the rhizosphere environment induced from underdeveloped root aerenchyma of rice at the seedling stage is one of the factors limiting rice growth. Different kinds of aerenchyma stimulants (sodium nitroprusside, sodium selenite and sodium hydrosulfide) were used to determine the biomass, nitrogen accumulation, root aerenchyma development (porosity), root external morphology, and rhizosphere dissolved oxygen at the seedling stage under hydroponic cultivation. The results show that all treatments can enhance rice growth by stimulating the development of root aerenchyma, and improve rhizosphere oxygen content at the seedling stage. Among all stimulants, 0.01 mmol/L sodium selenite treatment has the best effect, rice dry matter, nitrogen accumulation, root porosity and rhizosphere oxygen content are significantly increased by 36.7%, 16.1%, 57.3% and 39.9% compared with control treatment (without stimulant addition), respectively. An obvious threshold (42%) is observed in root porosity no matter with rice growth or nitrogen accumulation at the seedling stage. When root porosity is less than the threshold value, rice dry matter and nitrogen accumulation are significantly increased 8.8 and 0.2 mg per plant for each 1% increase in porosity, respectively. When porosity is more than the threshold, the above indicators are both rapidly decreased. Therefore, a suitable concentration of aerenchyma stimulant can alleviate the inhibition of rice development caused by insufficient dissolved oxygen in the rhizosphere environment at the seedling stage, by increasing the root oxygen loss of roots, which provides a new way for improving rice nitrogen use efficiency.