Researches,such as measurement of doublebeta decay in nuclear physics,neutrino measurement in particle physics and dark matter directmeasurement in new physics,which need critical environments which radioactive background should be extremely low can be called ultra-low Researches, such as measurement of doublebeta decay in nuclear physics, neutrino measurement in particle physics and dark matter direct measurement in new physics, which need critical environments which radioactive background should be extremely low can be called ultra-low