Given that the Hawking radiation from celestial black holes is extremely weak and thus difficult to be detected practically, a series of analogue black holes have been constructed to observe the relevant analogue Hawking radiations in the laboratory. In this paper, based on the critical behavior of group velocity of the microwave signal propagating along a controllable composite right/left-handed transmission line, we theoretically demonstrate that an electromagnetic black hole can be constructed in the co-moving coordinate system; in the velocity space, its horizon is at the point, where the electromagnetic wave propagation group velocity equals to the propagation velocity of the voltage solitary wave. With the typical experimental parameters, the Hawking radiation temperature of such an electromagnetic black hole can be estimated as ∼ 30mK, and thus the radiation could be detected, in principle, by the current low-temperature experimental technique.