The in-situ inspection technology of thermal properties of building wall is an important technical guarantee to achieve the goal of building energy conservation. However, there is still a lack of fast, simple, and accurate unsteady-state detection method under natural conditions. This paper focuses on the thermal performance test and analysis method of building wall under natural condition. Two frequency domain analysis methods were developed for the thermal conductivity, as well as volume specific heat and thermal inertia of homogeneous wall along with the harmonic reaction method and the frequency domain analysis theory. The frequency response relationship between the internal and external surface temperature waves and indoor air temperature waves was established, and the relationship contains thermal performance parameters of wall. The thermal conductivity and specific volume heat of wall can be solved by using the response relation. Numerical simulation verification of the method was completed by using ANSYS software and the experimental verification by using wall insulation materials were accomplished in the laboratory. The maximum relative error of numerical simulation results is 1.48%, and that of laboratory experiment results is 8.75%. The implications of these results with respect to the influence on the in-situ inspection technology of building wall are discuss.