With the climate conditions in northwest Qinghai and the characteristics of local rural adobe buildings,the harmonic Fourier series to express the outdoor sol-air temperature function is adopted as outside boundary conditions for wall thermal analysis. Based on the theory of wall thermal system,time lag and decrement factor of the adobe wall before and after the thermal insulation renovation are calculated with Matlab. The net heat loss of the wall and the inner surface fluctuation temperature are calculated by the harmonic reaction method. The results show that the heat loss of the wall is reduced to a greatly extent after the insulation renovation,and the energy saving rate of the wall reaches up to 74% and the inner surface temperature has an increase from 3.4- 4.7 ℃,which not only improves the indoor radiation field temperature,but also makes the indoor radiation field be more uniform,thus increasing the thermal comfort of the interior personnel. At the same time,the research and analysis for our new residential design provides a quantitative basis and scientific understanding.