An analysis is made of the types of electric surges that invade weak current equipment, and the problem that the threshold voltage and residual voltage of Zn0 surge protection devices, which are commonly used in lightning protection engineering, tend to be high and cannot protect weak current equipment well. It is proposed that the commonmode and differentialmode components of the lightninginduced overvoltage should be treated separately while protecting. Isolating transformers are introduced as antisurge devices into the lightning protection engineering of weak current equipment, considering the characteristic that there is only electromagnetic coupling and no direct electrical channel between primary winding and secondary winding to isolate the commonmode voltage. The magnetic saturation and magnetic creeping phenomena of iron cores are used to restrain and reduce the differentialmode components of the lightninginduced overvoltage. Using the isolating transformer as essential protection unit in the Zn0 surge protection device to cover the disadvantage of Zn0 surge protection device, the weak current equipment can be protected. The effect of lightning protection is proved through practical application.