Based on underwater unit short/open circuit failure modes, a method for analyzing the reliability of constant current remote power feeding system of cabled seafloor observatory network was proposed. According to system power supply and structural properties, the system was divided into different links and segments. Influence on power supply state of the links and observation equipments by unit failures in different position was studied in detail. The causes of leading system and link cannot be conducted and observation equipment cannot be operated were summarized, and the probability of different fault occurrence was analyzed, then power supply reliabilities method of system, links and observation equipments were obtained. Through example analysis，the general law of the three kinds of power supply reliability needs comprehensive considerations in system construction and design phase.