Computer network attack as a method of warfare has been casting confusing mist upon the application of jus in bello in recent years. Observing that many states are implementing more and more aggressive cyber strategy, an examination of applicable law regulating cyber warfare becomes crucially important. This paper attempts to review the traditional norms of jus in bello and explore their defects in the context of cyber space. Accordingly, in the fist part the author provides the brief introduction of conventional jus in bello and its application in kinetic warfare. Further, the second part explains some special natures of the use of cyber tools in warfare and the third part analyzes the problems of applying the traditional jus in bello in cyber space. Last but not least, the final part gives some conclusive remarks and points out the solutions would be to initiate more international co-operation.