Abstract: Nature reserves play an essential role in maintaining biodiversity and ecosystem services. The spatial datasets on nature reserves, ecosystem services, and biodiversity priority conservation areas of Three Parallel Rivers Regions were compiled to assess the maintenance of biodiversity and ecosystem services within nature reserves by identifying the key areas providing ecosystem services and applying spatial overlaying analysis. The results showed: ① Biodiversity features were well covered by nature reserves, with three portfolios of biodiversity priority conservation areas receiving more than 17% protection; ② Regulating services were not sufficiently protected, and the coverage for the key areas of carbon sequestration and soil retention was lower than the average protection rate (12.65%). The coverages for the key areas of provision service and culture service were more than 17%; ③ In general, nature reserves contribute significantly to the maintenance of biodiversity and ecosystem services in the study area, but there are many conservation gaps remaining to be filled in the future. Our study can provide scientific support for regional-scale planning of protected area systems.