Composite insulator has been widely used in power system due to its excellent flashover endurance capability, but the common umbrella-type composite insulator is easily been bridged in icing condition, and the insulating properties of iced composite insulator decrease obviously. In recent years, the flashover accidents of transmission lines and substation insulators caused by icing have been a serious threat to the safe and stable operation of power system. A lot of work has been done on the flashover characteristics of iced composite insulators in China and abroad, but most tests are focused on short strings. Only few researches on EHV and UHV full-size complete string insulator. This paper carried out icing flashover tests for four 750 kV composite insulators with different umbrella-types. The results show that the icing process and final icing status are different after adding large umbrella to composite insulator； the flashover voltage of composite insulators with 7/9/10 large anti-icing umbrellas is 12.3%, 25.8% and 27.7% higher than that of standard composite insulatorsm, respectively. The flashover voltage increases along with the number increase of anti-icing umbrellas, while has a saturated trend. The anti-icing umbrella optimization of 750 kV composite insulators should choose a reasonable anti-icing distance.