Base on broad collected data and experimental analysis, the carbon dioxide exchange between crop systems and atmosphere was studied in Guangzhou City. Both the CO2 absorb ability in all crop systems net productivity process and carbon sink function had been analyzed. Results showed that the CO2 absorb ability in the eight Crop systems net productivity process was 4 032 366t·a-1; the amount of CO2 outlet in the soil was 3981753t·a-1 , less than the CO2 adsorb ability, so that the whole crop system was a weaker carbon sink process in the atmosphere. The continue planting species such as Rice, sugarcane, cassava, and melon crop or high haulm crops have the characteristics of annually crop net productivity CO2 absorb ability bigger than soil CO2 outlet and this systems had bigger carbon sink function ability; the short haulm crop systems of peanut, soybean, flowers, and vegetable annually crops net productivity CO2 absorb ability less than soil CO2 out let, but also carbon sink source. The CO2 absorb ability of fruits and economic parts above ground bigger than that which growth under ground. Except of the CO2 absorb ability less than the soil CO2 outlet in the peanut during growth in procreate period, the other seven crops CO2 absorb ability were bigger than that soil CO2o outlet during procreate period. Most of crops during growth in procreate period had carbon sink function ability, and only in barren period showed the carbon source function phenomenon.