Dissolved manganese and iron are important elements as biological nutrients in marine and major tracers of probing hydrothermal activities and their evolution. Due to the urgent needs of the study of seafloor hydrothermal activities and the rapid development of supporting platform of underwater vehicles, such as AUV, ROV and HOV, the in-situ analyzing technologies of dissolved manganese and iron in deep seawater have been rapidly developed since the 1980s. The early development of Scanner and SUAVE can detect the high contents of manganese and iron in hydrothermal plumes simultaneously，but the problems of mutual inference between elements exist. Therefore, in situ analyzers for separate measurements of manganese and iron came into being. For the in situ manganese analyzers, ZAPS had a lower limit of detection, but it cannot be calibrated in situ because of the high pressure environment in deep sea; GAMOS series had the merits of in-situ calibration function, lower power consumption and long-time running, but relatively high detection limit caused them only applicable for detecting comparatively abundant manganese in hydrothermal environment. For the in situ iron analyzers, the modified ALCHIMIST can realize the detection of abnormally high content of iron around hydrothermal vents and low content of iron in normal seawater, but it can not be applied in the long-term observation yet because of the problem of high power consumption. However, the Fe-Osmo-Analyzer and CHEMINI with lower power consumption had a significant advantage in the matter of long-time running. With the widespread use of AUV/ROV/HOV and other underwater platforms and the rapid progress of seafloor observatory, the development of in situ analyzer for long-time observation will become an inevitable trend.