The high intensity proton accelerator of China Spallation Neutron Source adopts the method of charge exchange injection. A carbon foil strips two electrons of H^- into H⁺, and proton beams are multiturn-painted in the phase space of the rapid cycling synchrontron for acceleration to 1.6 GeV. A new-developed beam current transformer (H⁰CT) was installed at the I-Dump beamline to measure the incompletely stripped H^- and H⁰ particles, for the sake of an accurate measurement of the stripping efficiency, together with a study of the service life of the foil stripper with different thicknesses. To measure such extremely weak microampere beam current, in the development of the H⁰CT measurement system, we took into account the external interference and the noises from probes, cables and electronics. The new design has minimized the impact of environmental noise, improved the signal-to-noise ratio, and successfully measured the microampere pulsed current.