Abstract: The problems associated with LIRA3250 CO₂ gas monitor, such as outdated measuring method, complex structure, poor stability, etc, were improved. By comparing the technical performance, GMT221 CO₂ concentration sensor/transmitter with a measurement range of 0-3% was chosen as the measurement element of CO₂ monitor. The measuring and working principles and software design of the improved CO₂ gas monitoring system were also introduced. After improving, the measurement accuracy of CO₂ gas monitor reached ±0.02%, and its maintenance was convenient. The safety in production of CO₂ cut tobacco expanding workshop was ensured.