Nematodes represent key components of benthic ecosystems, highly-diversified and sensitive to environmental change and anthropogenic impacts. Field sampling for free-living marine nematodes was conducted at 29 sites in 10 intertidal regions along the coasts of Shandong Peninsula, China. The diversity, community structure, biological traits of marine nematodes and their relationships with environmental factors were analyzed, and the benthic ecological quality was assessed. Results showed that the average abundance of marine nematodes was 473.90±421.68 ind./10cm². A total of 247 species of marine nematodes belonging to 120 genera, 28 families and 4 orders were identified. The dominant genera were Daptonema (22.21%), Prochromadorella (11.49%), Oncholaimus (9.45%), Dichromadora (6.10%), and Bathylaimus (5.72%). Biological trait analysis showed that there were differences in nematode combinations for a single trait at the 29 sites. BIOENV analysis showed that the combination of temperature, salinity and sediment water content could best explain the differences in marine nematode community structure. The results of the DISTLM test for nematode biological traits showed that changes in environmental variables explained, to some extent, the changes in nematode traits. Based on c-p values and maturity index (MI), most sites can be classified as Moderate or Poor/Bad status. The present study indicates that marine nematodes can be used as good indicators for benthic ecological environment assessment.