Abstract: A prototype equipment composed of a NaI(Tl) detector and a small digit-gamma-ray spectrometer for on-line monitoring of ⁸⁵Kr was designed and set up, and a set of corresponding software was developed. The equipment has remote control and alarm functions, and it can remotely acquire, analyze and transfer data, work at the continuous or intermittent mode. The equipment working at the intermittent mode is more sensitive than working at the continuous mode. In laboratory, when the measurement time is 1 200 s, the detection limit of the equipment for ⁸⁵Kr is 3.4×10⁴ Bq/m³, and the judging limit is 1.7×10⁴Bq/m³. When the measurement time is 1 200 s, the gas pressure in the measurement container is more than 417 kPa, and the threshold value of alarm is set to be the detection limit, the equipment can work well, and the rates of both misinformation and failure are less than 0.1% for ⁸⁵Kr concentration of more than 8.1×10⁴Bq/m³.