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Since the accident of Fukushima Daiichi nuclear power plant, the environmental radiation dose was increasingly concerned as a global issue. In Taiwan, the detection capability of the all calibration laboratories is just about 50 times the naturally occurring environmental radiation for environmental radiation protection detectors. Undoubtedly the use of environmental radiation detector shows relative low performance in accuracy and the public are very sensitive to the amount of environmental radiation. Thus, the National Radiation Standard Laboratory (NRSL) of the Institute of Nuclear Energy Research (INER) designed a multi-source of low air kerma rate calibration system to respond to the measurement and calibration needs in Taiwan. The system was verified to meet the needs of measurement and calibration through a series of evaluations and comparisons based on ISO 4037-1 criteria (ISO 4037, 1996). This environmental-level dose rate measurement and calibration system contains three radioactive sources respectively penetrating by sets of filter of three different thicknesses and then producing radiation fields of three different strengths. A total of nine standard radiation fields are provided with intensity ranges from 1746.6 μGy/h to 0.092 μGy/h, and the expanded uncertainties of the system were from 1.02% to 5.77% (k = 2). • A pressure-adjustable 10 L-nitrogen-filled ion chamber was used for air kerma determination. • A multi sources irradiator produced the irradiation field from 0.06 to 1.25 MeV gamma rays and 0.1–∼1700 μGy/h. • The tunnel-shaped shielding could reduce background interference to one tenth at the reference point. • A movable collimator and multi filters devices respectively adjust the suitable field size and air kerma rate. [ABSTRACT FROM AUTHOR]