In order to treat the low-temperature temporary aquaculture water of marine products, realize the synchronous power generation and desalination of the system and harvest algae biomass energy, a three-chamber biocathode macroalgae new microbial desalination fuel cell (MDC) was constructed. The power generation performance, desalination efficiency, denitrification effect and algae growth and COD degradation rate of macroalgae MDC in the treatment of temporary aquaculture water of marine products at different temperatures were experimentally studied. The results showed that in terms of power generation performance:under the load of 1 000 Ω external resistance, there was no significant difference in the voltage peak value of the system at 8 and 25℃, but there was great difference in the single power generation cycle and voltage stability time. The single power generation cycle was 228 and 158 h respectively, and the voltage stability time was 36 h and 84 h respectively; To achieve the same desalination rate, the time required at 8℃ was longer than that at 25℃. At low temperature, prolonging the operation time of the reactor can improve the desalination rate of MDC system. At low temperature, the removal rates of COD, NH₄⁺-N, NO₃^--N and TN in seafood temporary culture water could reach more than 60%. The macroalgae Ulra prolifera in MDC system grew slowly at low temperature, the net growth was low, and it still remained normal, and the photosynthetic efficiency F_v/F_m was 0.4-0.5. Low temperature affects the power generation and desalination performance of macroalgae MDC. However, the high COD degradation rate and denitrification effect show that the constructed macroalgae MDC can be used to treat low-temperature temporary aquaculture water of seafood.