Aiming at the problem of poor effectiveness of reagents when treating high-viscosity fracturing flowback fluid，the degradation experiments using chemical oxidation method，hydrolysis acidification method and enzymatic hydrolysis method were designed. Dynamic parameters such as viscosity，molecular weight，particle size distribution and the concentration of degradation products were measured through viscosity analysis， particle size detection， gel permeation chromatography， and sugar concentration detection. The results showed that when the guar gum was degraded with 10 g/L sodium hypochlorite using chemical oxidation method，the optimal viscosity reduction time was 30 min，and the viscosity was decreased to 4.22 mPa·s，while guar gum degradation remained incomplete，the particle size of the aggregates was greater than 2 μm and the degradation products with molecular weights was around 80×10⁴ Da，predominantly containing saccharide structures. Moreover，the increase of the sodium hypochlorite concentration could not enhance obviously the viscosity reduction effects. When the guar gum was degraded with 10 g/L activated sludge using hydrolysis acidification method，the viscosity reduction rate was slow during the initial stage of hydrolysis acidification but the complete viscosity reduction was achieved within 24 h. The particle size of the aggregates was approximately 0.21 μm and the molecular weights of the degradation product exhibited two-stage decline patterns，demonstrating "long-term effectiveness" characteristics. When the guar gum was degraded with 10 mg/L enzyme using enzymatic hydrolysis method，the viscosity was decreased to 5.43 mPa s within 10 min and the complete viscosity reduction was realized within 15 h. The molecular weight of the guar gum decreased to 160×10⁴ Da within 0—2 h，and the guar gum was completely transformed into small-molecule saccharides after 15 h. At the same time，the aggregates was approximately 0.19 μm. Compared with the control group，enzymatic hydrolysis caused minimal changes in chemical oxygen demand （COD） contributed by saccharides and total solution COD， indicating that the enzymatic hydrolysis reaction had strong selectivity and outstanding viscosity reduction effect on macromolecular guar gum，which was a better choice for the pretreatment process of fracturing flowback fluid.