Abstract: A hard x-ray (HXR) spectrometer has been developed and implemented on the ENN Xuan-Long 50U (EXL-50U) spherical torus to study runaway electron (RE) dynamics. The diagnostic system features adjustable viewing geometries and optimized shielding designs, ensuring reliable operation under high-parameter plasma conditions. By utilizing LaBr₃:Ce detectors with millisecond temporal resolution, both thin-target and thick-target bremsstrahlung spectra have been measured during plasma discharges. The system demonstrates the feasibility of investigating RE behavior through γ-ray spectroscopy in compact fusion devices, with potential applications in next-generation spherical torus.