Distribution transformer in 10 kV power distribution area is one of the most important equipment in distribution network． However，it is often be damaged by lightning in the area with more lightning activities． According to the typical design and the field investigation，the electromagnetic transient simulation model for lightning direct striking and lightning induction is established，and the lightning overvoltage of high voltage side insulation on distribution transformer is analyzed． The results are as follows: After lightning directly striking conductor，the voltage suffered by transformer insulation is the sum of the residual voltage of lightning arrester and the voltage of ground lead． The amplitude of overvoltage easily exceeds the standard lightning withstand voltage，which is 75 kV． Because the energy induced by lightning is small，the probability that overvoltage amplitude exceeding the standard lightning withstand voltage is very small． The preventive effect of adding lightning arrester on lightning direct overvoltage is studied． It is found that lightning arrester can greatly reduce the amplitude of overvoltage． If the electric distance between the arrester cross － arm and the transformer support is shortened on this basis，the probability of transformer damage can be greatly reduced