The deep-sea in-situ nuclear radiation detector can operate in the in-situ environment by itself after being configured by the mother ship. At the same time, after the instrument is salvaged and recovered, the mother ship needs to complete the docking and data recovery functions, and the data readout between the detector and the host computer on the mother ship becomes a key issue. Aiming at the compatibility and scalability problems existing in the current spectrometer readout equipment, this paper designs a data read-out method for the deep-sea in-situ nuclear radiation detector. The RS485 and LVDS physical layer are used in hardware to ensure the stable and reliable data readout spectrometer. The MODBUS protocol application layer is used to improve compatibility and scalability spectrometer. By building a laboratory test platform, the overall function of the system, and the bit error rate, eye diagram of the physical layer are tested. The results show that the method can realize the stable and reliable data readout of the deep-sea in-situ gamma detector. In the low-speed mode and high-speed mode, the reading data rate of the detection instrument system is 115200bps and 40Mbps respectively.