To prove the promotion of urban green to mitigate the regionally predetermined heat stress on the local urban scale, comprehensive numerical simulations using ENVI-met v5.0.2 were carried out in an E-W street canyon considering the representative urban structure in Jeju, Republic of Korea, on the heatwave day of August 15, 2020. The simulations consisted of 10 combinations of urban green infrastructure: street trees, grass, facade, and roof greening. Compared to the bare condition, combined green infrastructure led to the maximum reduction in mean air temperature (ATa) by 2.1 K, mean radiant temperature (ATmrt) to 25.3 K, and physiological equivalent temperature (APET) to 16.1 K. Street trees exhibited the greatest effect on the ATmrt and APET as a measure of human thermal comfort. The combination of various green infrastructures has a larger impact on ATmrt on the Sfacing sidewalk compared to the N-facing sidewalk, with a mean ATmrt of 21.2 K for the S-facing sidewalk and 8.0 K for the N-facing sidewalk. Green infrastructure brings about indoor ATa by 1.5 K at the N-bordering building. As relevant design guideline to reduce human heat stress in urban areas, the simulation results provide urban/landscape planners the quantitative effect of combinations of green infrastructure.