The working principle and design structure of the Solar Irradiance Absolute Radiometers(SIARs) developed by our research group is introduced. The radiometer offers its two improvements in burying the electrical heater winding into the wall of the cavity to improve the equivalence of electrical and radiative heating and in using thermo electrical temperature sensor to replace the usual resistance temperature sensor. The SIARs took part in International Pyrheliometer Comparisons(IPC) twice, and calibrated data are coincident well with World Radiometric Reference(WRR). Two SIARs have been put on PhysikalischMeteorologisches Observatorium Davos/World Radiometric Center(PMOD/WRC) to observe the sun together with the instruments of World Standard Group(WSG) for six years, and they show stable performance and uncertainty within 0.2%. Moreover, a Solar Constant Monitor(SCM) composed of three wide field of view SIARs mounted on SZ3 spacecraft has been used to measure solar irradiance for five months, obtained data are coincident with those of ACRIM in 0.2%. From June 2008, a Solar Total Irradiance Monitor(STIM) made up of three SIARs has also begun to measure total solar irradiance on FY3 satellite for long term.