The continuous rise in global temperatures has impacted the outdoor thermal comfort, exercise safety, and physical health of elderly people. This study focuses on elderly individuals in typical activity areas of E'ling Park, Chongqing, using microclimate monitoring and questionnaire surveys. The physiological equivalent temperature (PET) is used as the evaluation index to examine the effects of sunny and cloudy days in summer on the thermal comfort of elderly people. The results indicate: (1) There are significant differences in thermal comfort across different spatial types under sunny and cloudy conditions. On sunny days, the thermal comfort ranking is: the waterside and the lotus pond fully covered by vegetation > the sports ground partially covered by vegetation and hard paving > the embassy gate in an enclosed space > the fully exposed View tower. On cloudy days, the ranking is: inside the embassy walls > the Xizhao Pavilion with a gentle breeze > the lotus pond > the sports ground. (2) The neutral temperature is 22.58°C on sunny days and 23.98°C on cloudy days, with a neutral temperature range of 20.61°C–24.53°C on sunny days and 22.32°C–25.65°C on cloudy days. (3) On sunny days, the PET values for elderly individuals are positively correlated with solar radiation and temperature, while on cloudy days, PET is influenced by solar radiation and temperature (positively) and wind speed (negatively). (4) There is no significant difference between males and females in thermal comfort perception, but on sunny days, elderly people with a higher BMI or pre-existing health conditions are more likely to feel discomfort. On cloudy days, elderly individuals participating in group activities feel less heat than those engaging in solitary activities. Finally, the study proposes strategies to improve the thermal comfort of elderly people.