Climate warming is one of the main characteristics of global climate change and has a significant impact on the structure and function of terrestrial ecosystems. Soil microbial biomass is a crucial component of soil ecosystem and plays an important role in biogeochemical cycles and energy flow in ecosystems. However, soil microbial biomass is highly sensitive to environmental changes, and increase in air temperature will significantly affect soil microbial biomass. Several studies have investigated the effect of warming on soil microbial biomass, but most studies have focused on the effect of short-term simulated warming on soil microbial biomass in ecosystems such as forests, croplands, and grasslands, whereas little is known about the response of soil microbial biomass to long-term simulated warming in wetland ecosystems. Therefore, an in situ simulated warming experiment was conducted in a wetland ecosystem on Eastern Chongming Island, China. Open-top chambers (OTCs) were applied to simulate climate warming. This study investigated the effects of eight years of continuous warming on soil microbial biomass carbon and nitrogen contents at soil depths of 0-40cm in a wetland on Eastern Chongming Island. The results showed that continuous warming significantly increased soil microbial biomass carbon and nitrogen contents. From surface to deep soil layers (0-10, 10-20, 20-30, and 30-40cm), microbial biomass carbon increased by 39.32%, 70.79%, 65.20%, and 74.09%, whereas microbial biomass nitrogen increased by 66.46%, 178.27%, 47.24%, and 64.11%, respectively. However, the effect of simulated warming on soil microbial biomass at different soil depths and in different seasons did not show a uniform trend. Long-term simulated warming significantly increased soil microbial biomass carbon and nitrogen contents at the 0-20cm soil depth in April and at 0-40cm soil depth in July, but had no effect on soil microbial biomass carbon in October, although soil microbial biomass nitrogen content also significantly increased at 0-40cm soil depth. The ratio of microbial biomass carbon to microbial biomass nitrogen significantly increased in July. Correlation analysis showed that soil microbial biomass carbon and nitrogen were not significantly correlated with soil temperature, soil water content, and total nitrogen in the OTC and control group. Soil microbial biomass carbon and nitrogen contents and the ratio of microbial biomass carbon to microbial biomass nitrogen showed a positive correlation with the soil organic carbon in the OTC, but showed a negative correlation with the soil organic carbon in the control group. Thus, soil organic carbon is an important ecological factor affecting the responses of soil microbial biomass carbon and nitrogen to long-term simulated warming.