Abstract: According to the characteristics of shale oil reservoirs in Jianghan Oilfield, namely low-middle porosity, low-ultra low permeability, complex geological structure and strong sensitivity of unconventional reservoir, a kind of fracturing liquid system of carboxymethyl hydroxypropyl guar gum (CMHPG) with low damage has been developed, and evaluation on the swelling property, temperature resistance, shear resistance, gel breaking performance, the damage to reservoir and the influence of inorganic cation on viscosity of base fluid of CMHPG has also been conducted. The experimental results show that when the concentration of CMHPG is the half of HPG's, the requirement for carrying proppant during fracturing can be met. In addition, the content of residue is low after gelout, and the damage to the reservoir is also reduced. The application of CMHPG for large scale fracturing in X well of Qianye area is successful.