The traditional chlorine disinfection can not effectively disinfect polluted water and may result in exces- sive residual chlorine.In order to solve this problem,ultrasonic field was used to enhance the chlorine disinfection of E. coli in drinking water,and the corresponding laws and features were investigated.Moreover,the optimal con- ditions for the synergy disinfection were determined.Experimental results indicate that (1) for the water with an initial E. coli density of about 10⁴ CFU/mL,a treatment with 59kHz and 90W ultrasonic for 5min at the room tem- perature may result in an E. coli logarithmic inactivation rate of 0. 9; (2) after a treatment in sodium hypochlorite solution with an active chlorine content of 9. 0mg/L for 30min,the logarithmic inactivation rate increases to 2. 57; (3) the synergic disinfection with the two above-mentioned treatment methods helps to obtain a logarithmic inacti- vation rate of 5. 02 and a residual chlorine content of less than 4mg/L,which meets the national standard well.