To effectively address high-temperature heatwaves and ensure the health and safety of outdoor workers, the physiological and psychological responses of outdoor workers under varying summer activity levels requires further clarification. An experimental study involving 16 subjects was conducted in moderately hot outdoor summer environments, focusing on two typical scenarios: differences in work intensity and alternating work-rest cycles. Human thermal response experiments and on-site questionnaire surveys were performed under changing activity levels. Through analysis of objective physiological parameters and subjective thermal perception dynamics, significant differences are identified in metabolic rate, heart rate, and mean skin temperature during rest periods after different activity intensities. However, no significant differences are observed in subjective thermal perceptions. The variation pattern of mean skin temperature during activity transitions follows an exponential function. Metabolic rate is influenced not only by activity intensity but also by environmental temperature. Canonical correlation analysis reveals a significant correlation between subjective thermal perception and objective physiological parameters during outdoor activity changes, with an effective canonical correlation coefficient R₁ (U₁,V₁) of approximately 0.98. Here, U₁ and V₁ represent the first pair of canonical variables derived from the two sets of variables: physiological parameter responses and psychological perception responses. Regarding physiological parameter responses, heart rate and mean skin temperature show high canonical loadings, indicating their suitability as key indicators for assessing outdoor thermal states. For subjective response characteristics, outdoor workers' overall thermal comfort is primarily determined by variations in perspiration sensation.