By using the method of deflecting the standard radiation and the IRTS (IR Target Simulator) radiation into IR spectroradiometer alternatively, the developed IRTSCS(IR Target Simulator Calibration System) can calibrate IRTS directly. IRTSCS is consists of a standard collimating unit, a radiation-deflecting device and an IR spectroradiometer. The standard collimating unit contains a standard blackbody working in temperature of 50℃～1050℃ and a collimator which main mirror is an off-axis paraboloid of aperture 300mm. The radiation-deflecting device is composed of a 465mm aperture of reflecting mirror and a rotating platform with locating precision of 5″. IR spectroradiometer adopts CVF (Circular Variable Filter) to disperse the incident radiation. It has three working spectral in the ranges of 1μm～3μm, 3μm～5μm and 8μm～14μm respectively. Testing datum of the three ranges show that the minimum spectral irradiance of calibration is lower than 10 -11W/cm2. The relative standard uncertainty of IRTSCS is 2% .