The formation conditions of jarosite in the system Fe2(SO4)3-K2SO4-H2O were studied. The results show that jarosite can be formed rapidly under normal temperature and pressure by controlling suitable pH value and Fe2(SO4)3 and K2SO4 concentrations. The pH value, temperature and concentration of Fe2(SO4)3 media are key factors affecting the formation of jarosite. At normal temperature, the precipitation of jarosite can be seen within 24 hours when the pH value is between 2.60 and 3.10, and a great quantity of jarosite is formed within 48 hours. At about 90℃, the pH value range forming jarosite extends to 1.20～3.10, and within this range, the rising pH value is advantageous to the formation of jarosite. High Fe2(SO4)3 concentration is also favorable for the formation of jarosite. Relative pure jarosite can be synthesized when Fe2(SO4)3 concentration is high (>0.05 M) and jarosite containing melanterite and colloid amorphous hydroxide vitriol iron can be formed when Fe2(SO4)3 concentration is low. The depositing process of jarosite canbe used to tackle waste water from mines and other industries and remove S, Fe and other toxic and harmful elements such as As, Cr, Hg and Pb in water. The achievement of rapid formation of jarosite under normal temperature and pressure presents a potential good application prospect in using the precipitation of jarosite colloid and its analogues as isolation mantle layers of mine tailing producing acid mine drainage