In order to save energy and reduce building energy consumption, the author pro­posed a study on the impact of composite polystyrene particle thermal insulation mortar on building energy consumption and thermal energy storage, take the ETIRS-C residence as the research object, through simulation calculation under different insulation mortar thickness, analyze the relationship between insulation thickness and energy consumption and thermal environment. According to the simulation calculation of room temperature, horizontally, the thickness of thermal insulation mortar in air conditioning season is not sensitive to the natural room temperature, there is a certain sensitivity to the natural room temperature in the heating season, in the longitudinal direction, the 30 mm thick insulation mortar is the jumping point, and the increase of the thickness of insulation mortar has no obvious effect on the natural room temperature. According to the simulation cal­culation of room energy consumption, the thickness of thermal insulation mortar is about 20 mm, and both heat and cold consumption have achieved good thermal insulation and energy saving effect, further increasing the thickness of thermal insulation mortar will have limited impact on energy consumption, which may be uneconomical and increase the cost and construction difficulty. Therefore, based on the aforementioned results, it can be considered that the thickness of thermal insulation mortar should preferably be controlled within 20-30 mm.