The existing building reconstruction methods exist after three-dimensional building modeling information is not complete, and the wall insulation performance improvement effect is not obvious. Therefore, a reconstruction method of existing residential buildings based on 3D simulation is proposed. This paper analyzes the present situation of energy consumption of existing residential buildings, analyzes the fuzziness characteristic in the process of testing the thermal performance of existing residential buildings by the method of spatially distributed fusion and feature extraction, uses the fuzzy equilibrium scheduling method to decompose the fuzziness characteristic scale of the thermal performance of the thermal insulation of existing residential buildings, and optimizes the design of the thermal performance of the thermal insulation transformation of existing residential buildings. The 3D simulation software is a 3D modeling tool named 3DS Max. The real-time simulation software Unity3D engine is used to reconstruct the building scene and complete the reconstruction of existing residential buildings. The experimental results show that the information integrity of the building model reconstructed by 3D simulation technique is nearly 100%, and the insulation performance of the building wall is better.