A packing box suitable for an electronic device is provided. The packing box includes a box body and a box cover. The box cover is assembled on the box body and at least one part of the box cover is separable from the box body. The electronic device is accommodated between the box body and the box cover. When the box cover is separated from the box body, a predetermined function of the electronic device is triggered correspondingly with separating the box cover from the box body to actuate a trigger component of the electronic device. An electronic assembly and a method of opening an electronic assembly are also provided.