Summary Phase change materials (PCMs) attached to building envelopes have been widely investigated, but there are rare studies to evaluate the influence of micro‐environments of PCMs. This paper, therefore, aims to study the action mechanism of PCMs under the micro‐environment systematically and provides the optimization of PCMs parameters, to realize a further reduction in building energy use. Simulation results indicate that a big difference in the heat transfer of envelopes appears in different orientations due to differences in solar radiation. Then, the optimal transition temperature Tp and amount of use of PCMs increase with the increase in solar radiation intensity Isr. Compared with other envelopes, the west‐facing wall and roof need higher Tp and amount of PCMs, under Isr from 400 to 1000 W/m2 the optimal Tp increases from 28 to 34°C with a difference high up to 6°C. The result also shows that the building energy‐saving of optimal PCMs parameters would rise by 16.6% compared to the fixed PCMs parameters. Optimal transition temperature for each building orientation under different solar radiation intensity.