Simulated gel-breaking flowback fluid was prepared by four methods. By investigating the influence of molecular weight change, the relationship between molecular weight distribution and viscosity,residual thickener on circulating fluid during the degradation process, the degradation mechanism of the thickener and the limiting factors for recycling of the gel-breaking solution are given. The results show that the viscosity of the gel-breaking solution was qualified, and the molecular weight decreased to 1/2 of guar gum. The oxidant acted on α-1,6 acetal bond preferentially in the initial phase of the gel-breaking, the content of galactose in the gel breaking liquid increased, and the ratio of mannose to galactose in the residue was 4.5:1; the viscosity of the fracturing fluid prepared with the residual thickener content above 0.3% decreased obviously,and the fluid was not shear resistant. The viscosity of the conventional oxidized gel-breaking solution did not reach the standard, both the residual thickener concentration and the cross-linker consumption are increased, and the gel breaking was more difficult. The molecular weight of the gel-breaking solution used in the second cycle is 251 ×10⁵, which is much larger than the 2.8 ×10⁵ of Guar gum.