Tamarix chinensis is a dominant species in both the Yellow River Delta Natural Reserve and Changyi National Marine Specific Protection Area, Laizhou Bay, China, and plays an important role in wetland ecosystems. We investigated the relationship between T. chinensis and environmental factors, and the influences of T. chinensis on understory plants. We selected four T. chinensis communities with different hydrologic conditions and salinities in the Yellow River Delta Natural Reserve and the Changyi National Marine Specific Protection Area. The results showed that the growth of T. chinensis was negatively correlated with soil salinity. Generally no fertile island effects or salt island effects of T. chinensis on herbaceous plant communities were found in the coastal area of Laizhou Bay, China. In areas with high salinity, T. chinensis provided nursery effects for understory herbaceous species, increasing species diversity and enhancing plant growth. In low-salinity environments, T. chinensis appeared to restrain the growth of understory plants. This study observed different influences of T. chinensis on herbaceous species between the Yellow River Delta Natural Reserve and Changyi National Marine Specific Protection Area, providing scientific basis and theoretical foundation for investigating plant distribution and ecological community succession in Laizhou Bay, China.