The extraction of Pr3+was studied by using heptane containing bis(2-ethylhexyl)phosphinic acid in sodium perchlorate,chloroacetic acid and citric acid medium,respectively. The effects of extraction equilibrium time,different mediums,PIA-8 concentrations upon extraction Pr3+ and that of concentration of back extraction agent on back extraction rate of Pr3+ were discussed. The composition of the extracted compound was shown to be La(HA2)3.The pH1/2 values of La3+,Ce3+,Pr3+,Nd3+,Sm3+ and Eu3+ in different mediums were determined,it is 3.69,3.30,3.16,3.10,2.68 and 2.54 in sodium perchlorate medium respectively,3.65,3.27,3.12,3.08,2.66 and 2.50 in chloroacetic acid mediums,respectively,4.34,4.26,4.11,3.91,3.57 and 3.38 in citric acid mediums,respectively.