The atomic relaxation time of a hydrogen atomic clock is the time required for atomic system after the selected state removing the atoms of the ground state hyperfine energy level (F = 0, m_F = 0) and (F = 1, m_F = −1) state to change from the (F = 1, m_F = 0) state to the (F = 0, m_F = 0) state until the atomic system reaches equilibrium. This parameter reflects the lifetime of atoms and directly affects performance of hydrogen clock. In order to measure the relaxation time of active hydrogen atomic clock and thus evaluate its performance, hydrogen atomic relaxation test system was established, which was composed of a Raspberry Pi (RPI), signal generator, digital attenuation, microwave detection, and data acquisition circuits. RPI generates timing signal to control the relay of digital attenuator and ionization source power supply circuit, so as to control the opening of microwave detection signal and the on-off of atomic beam current. The relaxation time of the hydrogen atomic clock is measured by data fitting of the acquired free induction decay signals. This method is important for optimizing the atomic linewidth and improving the performance of the active hydrogen clock.