In this study, the solubilities and densities of a ternary system (NaH2PO4 + CO(NH2)(2) + H2O) at 298.15 K was investigated using isothermal solution saturation and moist residues. According to the experimental results, the phase diagram and the diagram of densities versus composition were plotted. It turned out that there were one cosaturated point (CO(NH2)(2) + NaH2PO4 center dot 2H(2)O), two univariant curves, and two crystallization regions corresponding to NaH2PO4 center dot 2H(2)O and CO(NH2)(2) in this ternary system. The system belonged to a simple eutectic type, in which no double salt was formed. This research filled the blank of phase diagram in this ternary system and demonstrated the absence of double salt in the system.