In this study, the Yb_(1-x)Ca_xFeO_3(0≤x≤0.3) nanocrystalline powders were prepared by sol-gel method. We used the method of quantitative analysis to research the gas-sensitive properties for Yb_(1-x)Ca_xFeO_3 to CO_2. Also, we investigated the effects of various factors on gas sensing properties by simple variable method. The doping of Ca could not only decrease the resistance of YbFeO_3, but also enhance its sensitivity to CO_2. When the Ca content x=0.2, Yb_(1-x)Ca_xFeO_3 showed the best response to CO_2. The response Rg/Ra to 5000 ppm CO_2 for Yb_(0.8)Ca_(0.2)FeO_3 at its optimal temperature of 260 °C with the room temperature humidity of 28%RH was 1.85. The response and recovery time decreased with an increase of the operating temperature for Yb_(0.8)Ca_(0.2)FeO_3 sensor to 5000 ppm CO_2. Furthermore, with an increase of CO_2 concentration from 1000 to 50000 ppm, the response time of Yb_(0.8)Ca_(0.2)FeO_3 became shorter, and meanwhile the recovery time was longer. CO_2-sensing response for Yb_(0.8)Ca_(0.2)FeO_3 increased with the increase of relative humidity. The response for Yb_(0.8)Ca_(0.2)FeO_3 in the background of air(with the room temperature humidity of 39%RH) at 260 °C could reach 2.012 to 5000 ppm CO_2, which was larger than the corresponding value(1.16) in dry air. In this study, the Yb_ (1-x) Ca_xFeO_3 (0≤x≤0.3) nanocrystalline powders were prepared by sol-gel method. We used the method of quantitative analysis to research the gas-sensitive properties for Yb_ (1-x) The doping of Ca could not only decrease the resistance of YbFeO_3, but also enhance its sensitivity to CO_2. When the Ca content x = 0.2 , Yb_ (1-x) Ca_xFeO_3 showed the best response to CO_2. The response Rg / Ra to 5000 ppm CO_2 for Yb_ (0.8) Ca_ (0.2) FeO_3 at its optimal temperature of 260 ° C with the room temperature humidity of 28% RH was 1.85. The response and recovery time decreased with an increase of the operating temperature for Yb - (0.8) Ca 0.2 FeO 3 sensor to 5000 ppm CO 2. Further, with an increase of CO 2 concentration from 1000 to 50000 ppm, the response time of Yb_ (0.8) Ca_ (0.2) FeO_3 became shorter, and meanwhile the recovery time was longer. CO_2-sensin The response of Yb_ (0.8) Ca_ (0.2) FeO_3 in the background of air (with the room temperature humidity of 39% RH) at 260 ° C could reach 2.012 to 5000 ppm CO_2, which was larger than the corresponding value (1.16) in dry air.