Rubber expansion joint at condenser throat is crucial for the stable operation in a nuclear power plant, but its selection and application are constrained by the lack of effective evaluation method. This paper proposed evaluating the structure and performance of rubber expansion joint based on its actual operating conditions, including chemical structure analysis, micro-morphology observation, mechanics performance testing, lateral offset detection, corrosion and erosion resistance assessment as well as hot air and ozone aging performance testing, and predicting the service life of the same on the basis of the relationship between the variation of elongation at break in air and temperature. Then the structure and performance characteristics plus the service life of rubber expansion joint in a nuclear power plant were studied with the abovementioned system, which effectively reflects the application characteristics of rubber expansion joint. The investigated rubber expansion joint exhibits moderate hardness and good fibrous curtain layer strength, interlayer bond strength, compression property, lateral offset performance, corrosion resistance and low-temperature resilience. However, the tensile strength and the elongation at break need improving compared to those of pure neoprene rubber. The fatigue life of the rubber expansion joint is closely related to the maximum strain and its heat (ozone) aging resistance is good with a service life of around 32.6 years at ambient temperature (around 25 ℃) and 8.1 years at operating temperature (around 40 ℃).