The densities and viscosities for the tributyl phosphate (TBP) (1) + aviation kerosene (AK) (2) + phosphoric acid (PA) (3) system with the mass fraction of H(3)PO(4) in the range of (0 to 9) % and temperatures from (20 to 60) degrees C were measured. It is found that the measured viscosities are well-correlated with the temperature and mass fraction or H(3)PO(4) and were fitted to regression equations. The result shows that the effects of the mass fraction of TBP in the Mixture (TBP + AK) oil the viscosity of the TBP + AK + PA system is in the order of 91.5 % > 82.8 % > 73.7 % under the same ternperature and mass fraction of H(3)PO(4), and therefore, it is more appropriate to purify wet-process PA by solvent extraction with a mass fraction of TBP of 82.8 % rather than 91.5 % or 73.7 %.