The fractional crystallization process of high-saline wastewater is important for the sustainable development of coal chemical industry. This study mainly focused on the process investigation of Na2SO4 crystallization separation. The effects of heating temperature and stirring rate on the particle size distribution of anhydrous sodium sulphate (Na2SO4) crystals were investigated by batch-evaporation crystallization. Taking into account the product performance and the operating costs, the optimal operating conditions were determined to be 130 °C and 300 rpm. Granular Na2SO4 crystals with a purity higher than 99.0% were obtained. And the corresponding D0.10 was 309 µm. Moreover, the effects of impurity ions and organic matter on the preparation of Na2SO4 were discussed. The experimental results reveal that the addition of impurity, whether ions or organic matter, can lead to a decrease of D0.10. Specially, D0.10 increases with the increasing wt.%(K+), while D0.10 gradually decreases as wt.%(F-) increases. Furthermore, the influence level of organic matter on D0.10 was ranked as tributyl phosphate> 4-methyl-2-pentanone> dodecane> p-nitrophenol. The corresponding SEM images show that the addition of 10 mM of these four substances have little effect on the crystal morphology.