In order to solve the problem of mechanical impurities and the secondary damage caused by direct reuse of the fracturing flowback fluid of oil and gas fields，the natural high molecular weight guar gum flocculant CG-1 was synthesized by amination cation modification reaction of guar gum with 3-chloro-2-hydroxypropyltrimethyl ammonium chloride using propylene oxide as etherification agent. The effect of the cationic degree of CG-1，CG-1 dosage，the type and dosage of coagulant and the environmental pH on flocculation performance of the system were investigated，and the treatment effect of the flocculant CG-1 system on the field neutral and acid fracturing fluid flowback fluid was investigated. The results showed that when the dosage of flocculant CG-1 with the cation degree of 14% was 0.1%，the dosage of coagulant aids B（a kind of dicarboxylic acid）was 0.2%— 0.4%，the flowback liquid was settled for 20 min and reached complete flocculation. The flocculant system had wide applicability， which had good flocculation effect on both neutral and acid fracturing fluid flowback fluid. The flowback fluid after flocculation treatment could be directly used for field fluid preparation，and the operation success rate was 100%.