The invention, which relates to the nuclear measuring instrument field, discloses a modular digital nuclear measuring apparatus comprising a CPU, an IO board card, buses, a low-voltage unit for converting a 220-V alternating-current power source into a direct-current power source, and a special-purpose nuclear measuring board card. The IO board card consists of an input board card, an output board card, and a communication card; and the input board card, the output board card, and the communication card are connected with the CPU by buses. The special-purpose nuclear measuring board card is connected with the input board card. The low-voltage unit is connected with the CPU, the IO board card, and the special-purpose nuclear measuring board card and provides power for the CPU, the IO board card, and the special-purpose nuclear measuring board card. According to the invention, the modular structure and digitalization of the reactor nuclear measuring apparatus are realized; and requirements of low-temperature drift, high anti-interference capability, communication transmission, and value calculation of the nuclear measuring instrument can be met. The redundancy module is reduced, so that the universal module can be used repeatedly and module saving is realized.