Abstract: The deep layer of Gaoshangbao oilfield is a low-permeability reservoir with large pores and fine throats and high content of micro-structured heterogeneous.It is easy to cause particle migration.The characteristics about the damage of associated non crosslinking fracturing fluid to reservoirs were analyzed.The viscosity average molecular weight of the chickening agent is 3.8 million. The chickening agent belongs to polyacrylamide polymer which has long-chain dewatering group. The influence of viscosity of fracturing fluid to the formation damage proportion is great. When the viscosity of breaking fluid is 2.71 mPa·s, the static formation damage proportion is over 28.75%. When the viscosity of breaking fluid is 29.6 mPa·s, the static formation damage proportion is over 51.9%. By long-time flow back(12 h), it is obvious that the permeability is declined about 15%~20%, indicating that it is easy for the reservoir to cause particle migration. By means of nuclear magnetic resonance and mercury injection test, it is indicated that high molecule polymer is mainly blocking pore throat(radius is 2~9 μm), which is mainly contributed to permeability. By means of SEM, it is proved that the grainy polymer is adsorbed on the rocks and the quantity of pore throat is decreased. The residual is interlaced and focused on the entry of the core, and is reducing at the end of core. It shows that the damage of the fracturing fluid to the reservoir is mainly concentrated near the well. According to comprehensive research,it is considered that this fracturing fluid is not completely clean fracturing fluid. It is emphasized the whole breaking and low molecular weight.