1,5-Pentanediamine carbonate (PDAC) can be used as the raw material to prepare pentamethylene diisocyanate (PDI), a new biobased aliphatic isocyanate. The preparation of high-quality PDAC by crystallization is taken to be valuable for the preparation of PDI, and it can be used as an effective approach for the separation and purification of 1,5-pentanediamine from the biocatalytic system as well. In this work, the solubility of PDAC from 283.15 to 323.15 K in water and binary solvent mixtures was measured by the polythermal method, and the experimental solubility data were correlated and analyzed by the modified Apelblat equation and van't Hoff equation. In addition, three crystallization methods were investigated, and PDAC crystals were finally prepared with high bulk density, good flowability, and stability. It was found that the PDAC has two crystal forms, both existing as a spherical aggregate. They were characterized by scanning electron microscopy, Fourier transform infrared spectroscopy, powder X-ray diffraction, thermogravimetry and differential scanning calorimetry, and hot stage microscopy. Besides, the sensitivity of the two crystal forms to humidity and their transformation behavior were studied. Compared with form I, form II was proven to be the thermodynamic stable polymorph in the temperature range from 298.15 to 338.15 K.