In order to study the unsteady heat and humidity coupling transfer law of external thermal insulation walls and reduce the harm of moisture inside the walls, the typical external thermal insulation walls in Baoding City, cold areas were taken as the research object, and the exterior wall external insulation systems with cast-in-place concrete as the base layer and lightweight blocks as the base layer were compared horizontally by simulation. At the same time, from the two aspects of the setting of the vapor barrier layer and the installation of the air layer, the influence on the thermal and humid performance of the wall was analyzed. The simulation results show that, under winter conditions in cold regions, the cast-in-place concrete wall insulation layer is affected by moisture on the side near the outdoor, and the lightweight block wall insulation layer is mainly affected by moisture in the middle of the insulation layer and on the side near the base wall. The latter is seriously affected by moisture, and the maximum relative humidity of the insulation layer is 71.5% which is higher than the outdoor ambient relative humidity for a long time. After installing the vapor barrier, the moisture content of the insulation layer of the lightweight block system decreased by 17.3%, and the relative humidity of the insulation layer dropped to less than 50%. After installing the air layer, the thermal resistance of the cast-in-place concrete system increased, the average temperature of the wall on the coldest day of the heating period increased by 2.88 ℃, and the maximum relative humidity of the insulation layer during the heating period decreased to 34%, but the relative humidity of the summer insulation layer was increased, and the comprehensive effect was not good.