In China，35 kV power grid directly supplies to large customers，because of the complexity of the customers and the inadequate protection measures，there often occurs phase － to － phase faults which lead to the equipment damage． Taking the phase － to － phase faults which occurred in 35 kV side of a 110 kV substation in Sichuan power grid for 4 times as an object， the phenomenon of each fault is analyzed in detail，the causes of the failure are pointed out，and a treatment plan is proposed to avoid the repeated failures． The conclusion is of great importance to the prevention of 35 kV phase － to － phase faults．