Eh-ph diagrem of plutonium under standard temperature and pressure (STP) assumption have been made. The stability domain of water was described based on redox reaction of water with oxygen and hydrogen. Two pairs of lines which were almost pararel to each other were found. Redox reaction of plutonium has yielded four Nerst equation each of which was represented by a line one line was vertical as a result of non-redox reaction.The length of each line was dependent on the other lines. Two pairs of lines were overlapped to each other if the concentration of each species was 10-9 M. Eh-ph diagrams of plutonium with non-similar concentrations were also described.