The solubility of ammonium dihydrogen phosphate (MAP) in the water-methanol system is essential for antisolvent crystallization studies. To investigate the effect of methanol on the solubility of MAP in water, the sol-ubility of MAP in the water-methanol system was determined by dynamic method and static equilibrium method at temperatures ranging from 293.2 to 343.2 K at atmospheric pressure. Results showed that the solubil-ity of MAP increased with the increase of temperature and the increase of water mole fraction in the water-meth-anol system. The experimental solubility data were correlated with the modified Apelblat equation, the combined nearly ideal binary solvent/Redlich-Kister (CNIBS/R-K) model and the Jouyban-Acree model. The cal-culated results based on these three models were in very good agreement with the experimental data with the average relative deviations of 0.65％, 0.97％, and 5.38％, respectively. Simultaneously, the thermodynamic proper-ties of the MAP dissolution process in the water-methanol system, including Gibbs energy change, enthalpy, and entropy were obtained by the Vant Hoff equation, which can be used to assess the crystallization process.