To explore the effect of microecological preparations on the growth and stress resistance of Litopenaeus vannamei larvae, different amounts of Bacillus and Lactobacillus bacteria were added to the L. vannamei aquaculture water during seeding. Seven groups were established and the microecological preparations were added every 5 d. Bacillus concentrations in the Y1, Y2 and Y3 groups were 10 ppm, 15 ppm and 20 ppm, respectively, and the Lactobacillus concentrations in the R1, R2 and R3 groups were 20 ppm, 25 ppm and 30 ppm. The control (C) group had no microecological preparation added. Results showed that the Y2 larvae achieved the heaviest body weights, which were significantly higher than those of all other groups (P < 0.05), except for Y3 and R3 (P > 0.05). The body weights of the Y2 group were 27.18%, 11.97%, 27.18% and 23.58% higher than the weights of the C, Y1, R1 and R2 groups, respectively. Furthermore, except for that of the R2 group (P > 0.05), the survival rate of the R3 group was significantly higher than that of the C (34.86%), Y1 (21.49%), Y2 (17.60%), Y3 (15.75%) and R1 (15.75%) groups (P < 0.05). Microecological preparation addition also improved the stress resistance of L. vannamei larvae. Results showed that under stress conditions (60 min in fresh water and a sudden temperature change of 5°C), the survival rate in the two treatment groups was markedly higher than that in the C group (14.46% and 9.65%, respectively; P < 0.05). These results demonstrated that microecological preparations significantly enhanced the growth, survival and stress resistance of L. vannamei larvae.