Abstract: With the smart grid becoming a national strategy, the security and reliability of the high speed and integration optical fiber communication network has become a key problem we need to focus on. But the fiber converter widely used in the power grid has no protection from high power electromagnetic pulse. If it is interfered or damaged, the whole communication network and power grid may be threatened. To study this problem, the thesis presents the test and analysis on a kind of commonly used fiber converter. Through the high power microwave radiation tests, we found the fiber converter might be disturbed or damaged in a low electromagnetic environment. Through further coupling simulation analysis and mechanism study of typical semiconductor device, it is determined that the main energy coupling channel is heat emission holes, and the coupling energy in L band would be at least an order of magnitude greater than that in S band. Coupling energy works mainly on conversion IC chips by field-circuit coupling, and the intrinsic reason might be the latch-up effect of semiconductor devices.