The cavity microenvironment of indirect green façades (IGFs) influences building thermal performance. However, precisely simulating this environment remains a challenge. To address this, we employed OpenFOAM for computational fluid dynamics simulations, vegetation was modeled as a porous medium. A leaf energy balance model was used to solve leaf temperature and heat fluxes. We investigated the effect of leaf area density (LAD), cavity thickness, and solar radiation direction on the thermal performance of IGFs. The daily thermal effects of IGFs during summer in Shanghai, China were also explored. The results showed that (1) The IGFs on the windward side (0.07 m/s) and leeward side (0.14 m/s) achieved the highest wind speed reductions with the highest LAD and largest cavity thickness. (2) An IGF with high LAD and small cavity thickness effectively cooled the wall surface. The maximum wall surface cooling (16.93°C) was observed when the leeward side received the majority of solar radiation. (3) IGFs installed on the west side demonstrated significant cooling, with maximum temperature reductions of 3.21°C and 16.41°C within the cavity and on wall surfaces, respectively, in Shanghai, China. This research developed a new simulation framework for IGFs and provided insights for optimizing IGF design.