Problems like small swept volume and short effective period of CO2 huff and puff for single horizontal well in the fault block reservoirs with edge water. Laboratory physical simulation experiments is conducted to optimize CO2 injection volumes of huff and puff for a horizontal well group，and to analyze the performance of water controlling and oil increasing of CO2 huff and puff in the fault block reservoirs with edge water. A 3D physical model of a horizontal well group is designed to model the process of CO2 huff and puff for a horizontal well group. Changes of soaking pressure with injection volumes of huff and puff are analyzed and production performance during production period are discussed. Combined with physical properties of CO2 and high-temperature and high-pressure physical properties of crude oil and CO2 ，the impact of CO2 injection volume on CO2 huff and puff for the horizontal well group in the fault block reservoirs with edge water is understood and the CO2 injection volume under the experimental conditions is determined. Experimental results show that when the CO2 injection volume is increased from 0.07 PV to 0.14 PV，the decline of composite water cut of well groups drops from 0.72% to 5.93%，and increase of oil production rises from 31.4 mL to 148.7 mL. Increase of oil production through CO2 huff and puff is obvious by enhancing injection volumes. When CO2 injection volume is increased to 0.14 PV，the recovery increase is up to 22.36%，but cumulative gas production is up to 8 050 mL at standard conditions，and the gas utilization efficiency drops. The main mechanism of water controlling and oil increasing by CO2 is that the decrease of CO2 isothermal compressibility at certain pressure makes it possible to inject gas with relatively low energy loss and enlarge swept volume. Meanwhile，the crude oil intends to be more flowable with the increase of CO2 composition in the crude oil.The swept efficiency of the injected gas may be improved with the increase of injection volumes.