  The main scientific goal of the Gravitational wave high-energy
Electromagnetic Counterpart All-sky Monitor (GECAM) is to monitor various types
of Gamma-Ray Bursts (GRB) originated from merger of binary compact stars, which
could also produce gravitational wave, and collapse of massive stars. In order
to study the response of GECAM Gamma-Ray Detectors (GRDs) to high-energy bursts
and test the in-flight trigger and localization software of GECAM before the
launch, a portable GRB simulator device is designed and implemented based on
grid controlled X-ray tube (GCXT) and direct digital synthesis (DDS)
technologies. The design of this GRB simulator which modulates X-ray flux
powered by high voltage up to 20 kV is demonstrated, and the time jitter (FWHM)
of the device is about 0.9 $\mu$s. Before the launch in December, 2020, both
two GECAM satellites were irradiated by different types of GRBs (including
short and long bursts in duration) generated by this GRB simulator. The light
curves detected with GECAM/GRDs are consistent with the programmed input
functions within statistical uncertainties, indicating the good performance of
both the GRDs and the GRB simulator.
