Tropical or subtropical climates result in considerable heat stress in outdoor environments, which handicaps social activities in public spaces such as urban parks. This study aims to find out the effects of park planning factors on thermal environments. The research measured 18 urban parks around the city of Gold Coast in Australia from January to March 2018 which is the summer time of the Southern Hemisphere. Climate data were collected for each park, based on which park cooling intensity, mean radiant temperature and physiological equivalent temperature were calculated as thermal environment indicators. Meanwhile, park planning factors such as park tree coverage, park size and distance to major water bodies (the sea) were selected for multiple linear regressions with the thermal indicators. Our findings have confirmed that the park planning factors had significant effects on the thermal indicators. The effect of park tree coverage was most significant. This study provides important evidence and guidance for urban planning to create better outdoor thermal environments in parks to facilitate social activities.