The hydraulic fracturing（HF） behavior under CO

2

condition is a key scientific issue in CO

2

-enhanced geothermal system project. The granite specimen was taken from the quarry in Zhangzhou

Fujian province. HF experiments were conducted to investigate the effects of CO

2

and H2 O on the HF process and crack propagation by using a new independently developed hollow cylinder. This study reveals that with the decrease of the viscosity of the fracturing fluid

a greater number and more sinuous microcrack branches form in the fracture process. This indicates that CO

2

fracturing may b

e more conducive to the formation of the crack network

which helps to increase the heat exchange efficiency in the CO

2

-EGS projects. The fracture pressure of the specimen decreases with decreasing the viscosity of the fracturing fluid

which leads to the safe operation of the injection well with a lower value. The experimental results consist with the interaction mechanism of fluid rock from the convective heat transfer perspective

and its accuracy is verified.