Abstract: Based on the combination of theoretical calculation and experimental measure-ment, the study on the solvent in PCS nanoparticle preparation process by gas antisol-vent recrystallization was carried out. The PCS's solvent parameter is calculated withthe theoretical method, and some solvents such as cyclohexane, p--dimethyl benzene andtetrahydropyrane, are adopted according to the calculated result. The volume expansionof solvent with the solved CO_2, the solubilities of solvent in CO_2, and the PCS in solventare measured for the adopted solvents. The experimental results indicate that the per-formance of tetrahydropyrane is the best among the three solvents, and the PCS nano-particle with a average size of 2. 2 nm is prepared using the tetrahydropyrane as solvent.