Abstract: The ionization chamber tritium monitor is the most important online monitoring equipment for monitoring the concentration of tritium in the air. In order to solve the problem of quantity value transmission, the calibration technology of ionization chamber tritium monitor was studied. The laboratory calibration device of tritium monitor is established according to the mass flow method. The reference tritium gas for calibration is diluted and prepared by controlling the volume of standard tritium gas filled into the calibration device. The prepared reference tritium gas is used to calibrate the ionization chamber tritium monitor. At the same time, the influence factors of the calibration process on the calibration results are studied on the developed laboratory calibration device; the expanded uncertainty of reference tritium gas concentration prepared by laboratory calibration device is 3.2%-3.6%(k=2); when tritium activity concentration is 3.10×10³-1.98×10⁵ Bq/L, the response linearity of SP1400 tritium monitor to tritium gas activity is good(r²=0.999 3), the calibration factor is 0.97, and the standard synthetic uncertainty is 4.3%-5.0%. The laboratory calibration device of tritium monitor can prepare tritium gas with different activity concentrations. The calibration method is simple to operate and easy to popularize, which can meet the needs of tritium monitor calibration.