Based on current situation of mobile equipments earth devices, a new type of portable horizontal grid earth electrode has been designed. With the impulse ground measurement system, different number of earth electrodes responses to double exponential pulse current have been tested on cement grounds. Impulse waves of voltage and current have been gotten by experiments, and the curve of Transient Grounding Resistance (TGR) can be calculated. The analysis of discharging capacity of horizontal grid earth electrodes in time domain has great significance in the design of mobile equipments earth devices.