Water fracturing is widely employed as a reservoir-stimulating technology for the recovery of unconventional oil and gas. However, the process suffers from massive water consumption and environmental concerns. Therefore, alternative fracturing fluids are desired. In recent years, fracturing with CO2 was proposed to embracemultiple benefits, including carbon storage, enhanced recovery, etc. Herein, based on specially designed facilities and new analytical methodologies, we present multiscale and quantitative investigations on the fracturing mechanism and behavior of CO2 and water. It was demonstrated that because of the high leak-off of CO2, shear fractures can be readily induced, which facilitated the formation of tensile and mixed fractures, leading to effective fracturing, complex networks, and greater stimulated reservoir volume. Finally, a 4- to 20- fold increase in tight oil production could be achieved by CO2 fracturing in field tests with five wells.