Spaceborne active differential absorption is a more accurate method to monitor global carbon dioxide. The atmospheric pressure, temperature, humidity, surface reflectivity and the hardware system linewidth, filter bandwidth and so on all have influence on retrieval error. Among them, the surface reflectivity has unnegligible influence on retrieval error. Experimental results show that the spot footprint is smaller, separation distance is bigger, and geomorphology is more complex, the retrieval error will be bigger. When the spot diameter is 100 m and distance interval is 10 m, the absolute error of six geomorphies ranges from 0.0215×10－6 to 0.2134×10－6, which is controlled within 1×10－6. It has certain reference significance to the actual hardware design.