All the physical and chemical properties of soil are ascribed to surface charge of soil particles.Many processes taking place in the soil system are influenced by surface charge.Therefore,parameters of its electrochemical properties,especially the surface potent ial and the surface charge density,are of the most importance.However,there is no reliable method available in accurately determining these parameters until recently.Li Hang solved this issue in his study by deducing the relationship between average potential and surface potential in the double layer.By using his method,surface charge properties of acidic,neutral and calcareous purplish soils were studied in this paper.The total charge volume,surface potential,surface charge density,electric field strength on surface and SSA(specific surface area) were determined.The effect of electrolyte concentration,cation variety,temperature and pH on the surface charge properties was also studied.The experimental results show that:(1) in 2B1 type electrolyte system(Mg(NO₃) ₂),the surface potential is-0.16~-0.18 V,-0.17~-0.19 V and -0.18~-0.19 V and the surface charge density is -0.26~-0.44 cm^-2,-0.37~-0.59 cm^-2 and -0.58~ -0.67 cm^-2 for acidic,neutral and calcareous purple soil samples,respectively;(2) the surface potential of the samples decreases with the electrolyte concentration increasing,but the surface charge density,and the electric field strength increase slowly;(3) the surface potential in 2:1 type electrolyte system is about 50 percent as much as the one in 1:1 type(KNO₃),however,there is little difference found in the surface charge density,the electric field strength and SSA between the two types of electrolyte system;(4) the surface potential,surface charge density and electric strength decrease with the temperature rising.