A high resolution temperature gradient detection system based on manned submersible is proposed in view of the small changes in the temperature gradient of the sediment in the deepsea hydrothermal area and the difficulty of the fine underwater detection. The system mainly includes the temperature gradient probe and the electronic cabin, the probe and the electronic cabin are connected with water, the probe is equipped with high precision NTC thermosensitive components, and the electronic module is equipped with the precision signal conditioning circuit, the system control unit and the lithium battery module. In this paper, the signal conditioning circuit is designed in principle, which improves the system resolution, reduces the circuit drift and misalignment, solves the problems of poor interchangeability and weak output signal of NTC thermosensitive components. The system structure is analyzed by finite element analysis, the design structure is optimized and the weight of the system is reduced. Finally, the system test is completed in the laboratory. The system uses the calibration score of 005. The NTC thermistors at the temperature range is 0~5 degrees, the resolution is 0001 degrees, and the working water depth is 2 000~4 000 meters. The underwater test was carried out on a manned submersible in the Great Jubilee hot water area of the India Ocean in Southwest China. The experimental results show that the structure of the system is reasonable and can be worked together with the manned submersible, and the temperature gradient data of the deepsea sediment in the Great Jubilee hydrothermal area have been successfully obtained.