Abstract: Monoethylene glycol regeneration & desalination system is one of key units in deepwater gas development, often using evaporative crystallization and sedimentation theory to achieve high solubility salt (such as NaCl) removal. The main process parameters on the desalting flash tank, mainly optimized from the perspective of energy in the past, can only show the effects of process parameters on evaporation, but not directly show the effects on the crystallization and particles settling & separation. To study the main process parameters of flash separator as a crystallizer, the influence of temperature, pressure, and residence time on the crystal size distribution of NaCl in ethylene glycol solution was studied by laser diffraction particle size analyzer. The results showed that under the same conditions, the higher temperature, the more dispersive crystal size distribution and the smaller average particle size; the higher degree of vacuum, the more dispersive crystal size distribution and the smaller average particle size; too long or too short of residence time would cause the average crystal size to become small. For discussed solutions, optimized process parameters are that flash temperature is 140℃, pressure is -80 kPa, and the residence time is 5 minutes. The optimized parameters can achieve stable sedimentation separation and desalination by the verification of developed continuous experimental apparatus.