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Building energy consumption and building carbon emissions both account for more than 20% of their total national values in China. Building employing phase change material (PCM) for passive temperature control shows a promising prospect in meeting the comfort demand and reducing energy consumption simultaneously. However, there is a lack of more detailed research on the interaction between the location and thickness of PCM and indoor natural convection, as well as indoor temperature distribution. In this study, the numerical model of a passive temperature-controlled building integrating the developed PCM module is established with the help of ANSYS. In which, the actual weather condition of Beijing city is set as the boundary conditions and the indoor natural convection is simulated with the consideration of radiation model. The effects of PCM's thickness and location on the internal temperature field are analyzed and discussed. The results show that the room could maintain within the human comfort temperature range with the longest ratio of 94.10% and the shortest ratio of 51.04% as integrating PCM. In comparison, the value is only 26.70% without PCM. The room's maximum temperature fluctuation can also be improved; it could be lowered by 64.4% compared to the normal condition. When the quantity of PCM is sufficient, further increasing the PCM amount results in a temperature fluctuation reduction of less than 0.1°C and does not increase the comfort time. Placing PCM on the wall induces an apparent variation in indoor temperature along the vertical direction. Conversely, placing PCM on the roof can lead to a heat transfer rate difference of up to seven times. The optimal placement of PCM depends on the difference between the environmental and phase change temperatures. If the difference is positive, placing PCM on the roof is more effective; conversely, the opposite holds. According to the results over the entire cycle, PCM application on vertical walls yields better performance. The significant difference in natural convection caused by the same thickness of PCM but different application positions, coupled with the influence of air movement on the melting and solidification of PCM, further impacts indoor temperature fluctuations and comfort. This study can provide guidance for the application location and thickness of PCM, especially for scenarios where temperature regulation is required at a specific time. [ABSTRACT FROM AUTHOR]