EM50 polymer used in slickwater as drag reduction agents（DRA）makes the treatment of the fracturing flowback fluid more difficult. In this paper，Ligand-Fenton composed of environment-friendly chelating agent tetrasodium iminodisuccinate（IDS） and Fenton was used to reduce viscosity of EM50 solution. On the basis of single-factor design，response surface methodology （RSM）was used to research the best level and mutual effect of n（IDS）：n（Fe（Ⅱ）），Fe（Ⅱ）and H2O2 dosage affected on viscosity-reducing rate. The results showed that under neutral pH，the order of three influencing factors on the viscosity-reducing rate was n（IDS）∶n（Fe（Ⅱ））>Fe（Ⅱ）dosage>H2O2 dosage. Among these factors，Interaction between n（IDS）∶n（Fe（Ⅱ）），Fe（Ⅱ） had a signifigant impact on the oxidation efficiency. the predicted optimal conditions was obtained as follows：n（IDS）∶n（Fe（II）= 1.4，c（Fe（II））=0.3 mmol/L and φ（H2O2）=0.5%. Under this conditions，the average viscosity-reducing rate of the EM50 solution with mass fraction of 0.1% was 84.01%，which is compared with resulting in a final response，the relative deviation to the predicted value was 2.62%，indicating that the model was reliable and accurate. When being treated using chemical coagulation after viscosity reducing，the removal rates of SS and COD in fracturing fluid recovery were 94.9% and 89.2%，respectively