To understand the temperature distributions of large scale cable-stayed bridges and provide loadings for thermal effect analysis, thermal field characteristics for the 3^rd Nanjing Yangtze River Bridge were investigated based on temperature monitoring data. Layout of the temperature sensors was firstly introduced. Then, the variation law of component temperatures over time was studied, and the correlation between component temperature and ambient temperature was discussed under the condition of solar radiation. Next, features of temperature gradients for the tower and steel box girder (vertical and transverse) were analyzed. Finally, extreme values of temperature actions corresponding to 100-year return period were estimated by using generalized Pareto distribution. Results show that the steel box girder temperature was linearly correlated with the ambient temperature, and the gradient parameter in the fitting equation increased with solar radiation intension. The maximum vertical temperature difference for the steel box girder occurred in summer, and its distribution form was much similar to the descriptions in BS 5400. The largest transverse temperature difference for the deck was in winter, and its distribution form was in line with multi-line model. The maximum temperature difference of the tower occurred in winter with the magnitude of 9.94 ℃. Except for the vertical temperature gradient of the steel box girder, the estimated values of the other thermal actions were all larger than those in the codes. The thermal field analysis results of the 3^rd Nanjing Yangtze River Bridge may assist thermal effect simulation of steel cable-stayed bridges as well as support bridge design specification revision and bridge maintenance.