We experimentally compare the solar irradiance absolute radiometer (SIAR) measurement with the world radiometric reference (WRR) standard to improve the accuracy of instrument. The SIAR joined in the international pyrheliometer comparison (IPC) in 2000. The comparison results show that the calibration factors for SIAR to WRR are 0.999 220, 1.001 694, 0.998 334 and 0.997 439 in the 9th IPC, the 10th IPC, the 11th IPC and the 12th IPC, respectively. These results are added to the measurement uncertainty budget of SIAR. The repeatability of the SIAR-type absolute radiometers is also investigated. The relative error introduced by two SIAR-type absolute radiometers is within 0.25%.