The invention provides a portable nuclear instrument system signal detection and fault positioning device. The device comprises a shell, a power supply board, a main control board, a weak current signal acquisition board, a source range pulse signal acquisition board, a high voltage output board and a liquid crystal display board, wherein an accommodating cavity is formed in the shell; the power supply board, the main control board, the weak current signal acquisition board, the source range pulse signal acquisition board and the high voltage output board are all placed in the accommodating cavity; the liquid crystal display panel is fixed on the surface of the shell, and the power panel, the weak current signal acquisition board, the source range pulse signal acquisition board, the high voltage output board and the liquid crystal display panel are all electrically connected with the main control board; the weak current signal acquisition board, the source range pulse signal acquisition board and the high voltage output board are provided with corresponding HN terminals; and the HN terminal is arranged on the surface of the shell. According to the invention, when an abnormal signaloccurs, a fault section can be troubleshot through a segmentation test function of the device, so that troubleshooting and positioning are realized.