In order to investigate the contribution of basic food sources to Lateolabrax maculatus in three sub habitats of Jiuduansha salt marsh wetland in the Shanghai and to determine the stable isotope characteristics of carbon (δ¹³C) and nitrogen (δ¹⁵N) and the variation characteristics of basic food sources of this species, a survey was conducted in the mudflat, Scirpus mariqueter vegetation area and tidal creek from May to October in 2019. The results of one-way analysis of variance showed that there were no significant difference in δ13C among the three sub habitats. There were significant differences in δ15N between vegetation area and mudflat sub habitats, and there were significant differences in δ15N between vegetation area and the tidal creek sub habitat (P＜0.05). Increasing with body length δ¹³C and δ¹⁵N value showed an increasing trend, and δ13C value of L. maculatus in Jiuduansha salt marsh gradually increased each month, while δ15N value decreased sharply in July. The cluster analysis of monthly average δ¹³C and δ15N showed that July had little similarity with the other months (May, June, August, September, and October). The results showed that the composition and contribution rate of basic food sources in the three sub habitats are similar, and suspended particulate organic matter (POM) and Spartina alterniflora were the main carbon sources, followed by microalgae, Scirpus mariqueter and Phragmites australis contributed the least to the carbon source of maculatus. The contribution rate of POM decreased, while that of S. alterniflora increased with the increase in body length. With the growth of L. maculatus, the main food source for it changed from POM (＞70%) to POM (50%–66%) and S. alterniflora (32%–47%). The results showed that the feeding habits of L. maculatus changed in the juvenile stage. The contribution rates of carbon sources to L. maculatus in July were different from those in other months. The change was mainly caused by the sudden increase in the POM contribution rate and the decrease in the algae contribution rate. The internal reason may be affected by the Yangtze River runoff. Conclusion: there were no significant differences in the composition and contribution rate of basic food sources of L. maculatus among the three sub habitats, but there may be differences in the feeding in different sub habitats; During the growth process, the basic food source of of L. maculatus in the three sub habitats changed from POM to POM and S. alterniflora, which may be due to the change of feeding habits of L. maculatus during the growth process.