The research of the spatial and temporal distribution of the extinguishant concentration is necessary for the design of a fire extinguishing system. The detection technique based on the differential pressure principle is very suitable for the extinguishant concentration measurement. This paper focused on studying the effect of sensing structure on sensing performance. It was found that due to the solid sensing structure, the sensor had good stability and reproducibility, and the response/sensitivity would increase with the increase of the throat diameter of the critical flow nozzle and temperature, and with the decrease of the inner diameter and the number of the tubes of the vascular bundles, which were in good agreement with the theoretical prediction. For the response rate, it could be improved by increasing the throat diameter and decreasing the external diameter of the vascular bundles, but these also caused the great increase in the response fluctuation, which could lead to the decrease in measuring accuracy despite the improvement in response and sensitivity, especially for the high concentration. However, the increase of the temperature would efficiently reduce the response fluctuation while improving the response and sensitivity. The research results can provide good theoretical suggestions for the sensor design.