The present invention relates to a heat-insulating structural chassis of the pull-down windows for increasing the project as, more particularly, is an improved water-tightness and airtightness Sikkim as well as structural rigidity of the heat insulating structural chassis of the pull-down windows project. The present invention, insulation is installed on the inner and outer fixed frame (10, 20) provided in the outer wall side of the building, while opening the glass 50 Ventilate the indoor and outdoor air as well as projects a pull-down so as to insulate the indoor and outdoor windows in the structural chassis, insulating structural chassis of the windows are disposed on the indoor side inside window frame 70 for supporting one side of the glass (50); An outer window frame 80 is opposed to the inner window frame 70 for supporting the other side of the glass (50); Claim that is inserted into the inner window frame 70 and outer window frame 80, the fitting groove (71, 83) provided on each inner block the heat exchange between the inner window frame 70 and outer window frame 80 1 thermal bridges the barrier material (90); Fixing the inner frame 10 is provided on, exposed through the inner gasket 105 is provided at the upper end in contact with the inner window frame 70, the cover frame (100); Is provided on the outer fixed frame 20, the agent disposed in the exposure the cover frame 100, the first support frame 110, which is in contact with the outer gasket 87 is installed at the bottom of the outer window frame 80 .; A second thermal bridge barrier to block the heat exchange between the exposed cover frame 100 and the support frame 110, the fitting groove is inserted (103, 111) the exposure the cover frame 100 and support frame 110 provided on each inner side 120; And the second thermal bridge barrier material (120) to block the heat exchange between the indoor and outdoor of the between the first and second thermal bridge of the barrier material (90, 120) a spaced Sikkim as well as the first and second thermal bridge of the barrier material (90, 120) between include; bonded to the top and middle gasket 130 is in close contact with the bottom of the first thermal bridge of the barrier material (90).