Abstract: A protective case applied to assemble to a handheld electronic device is provided. The protective case includes an inner surface, an outer surface, a connector, a plurality of first detachable connecting structures, and a plurality of first electrical connecting structures. The connector is located at the inner surface to electrically connect to the handheld electronic device. The connector includes a plurality of signal transmitting pins. The first detachable connecting structures are arranged in a first array on the outer surface. The first electrical connecting structures are arranged in a second array on the outer surface. The first electrical connecting structures are electrically connected to the signal transmitting pins respectively.