Abstract: Two-year-old container seedlings of Lagerstroemia indica 'Zijingling' were used as experimental materials, and the '3414' fertilization experiment scheme was adopted, with the setting of three factors: nitrogen, phosphorus and potassium, and 4 levels of each factor, a total of 14 treatments. The effects of different treatments on the growth and nutrient accumulation of L. indica were studied, and the model of total increase of plant height and fertilizer effect of N, P and K was established. The fertilizer effect equation model was optimized by using frequency analysis method, and the optimized fertilizer application rate was obtained, which provided theoretical guidance and technical support for scientific fertilization of L. indica. The results can be seen as follows: 1) T₆ (N₂P₂K₂) had the best growth index, with the total increase of plant height, total increase of crown width, inflorescence length and width and flower diameter increased by 69.04%, 24.16%, 92.30%, 65.57% and 20.01%, respectively, compared with the treatment without fertilization (T₁); 2) The contents of total nitrogen, total phosphorus and total potassium in leaves increased with the increase of fertilizer application rate of nitrogen, phosphorus and potassium, respectively; 3) The correlation between the fitted fertilizer effect model of nitrogen, phosphorus and potassium application rates and the total increase of plant height reached a highly significant level, indicating that the model fitting was successful; the frequency analysis method was used to optimize the fertilizer effect model, and it was concluded that the fertilizer application rate of L. indica under the matrix ratio of this study was N: 13.70−17.60 g/plant, P₂O₅: 6.62−8.60 g/plant, K₂O: 7.25−9.12 g/plant when the total increase of plant height was more than 39.09 cm. With the factors of environmental protection and economic benefits of fertilizer put into consideration, the fertilization scheme obtained by frequency analysis method can be selected amid the cultivation of container seedlings of L. indica, which can significantly promote the growth of seedlings in a rapid manner.