This paper takes Spirodela polyrhiza as the experimental object to study the effects of the dilution multiple of aquaculture wastewater and the initial inoculation amount on the growth and crude protein accumulation of Spirodela polyrhiza, as well as the absorption and purification patterns of nitrogen and phosphorus nutrients in aquaculture wastewater by Spirodela polyrhiza. The results show that with the increase of the dilution multiple of aquaculture wastewater, the removal rates of NH4+N, NO3N, and PO43P by Spirodela polyrhiza gradually increase, and the absorption and purification of NH4+N by Spirodela polyrhiza is earlier than that of NO3N. With the increase of the initial inoculation amount of Spirodela polyrhiza, the removal rates of PO43P and NO3N both increase. When the initial inoculation amounts of Spirodela polyrhiza are 50% and 75%, the removal rates of NH4+N reach 97.6% and 94.1%, respectively. The crude protein content of Spirodela polyrhiza decreases with the increase of the dilution multiple of aquaculture wastewater. The highest growth amount and growth rate of Spirodela polyrhiza is achieved in the aquaculture wastewater diluted 20 times. Under the conditions of 20 times dilution of aquaculture wastewater and an initial inoculation amount of 75% of Spirodela polyrhiza, the annual protein yield of Spirodela polyrhiza can reach 0.91 t/hm².