Abstract: The phase diagram of the title quinary system at 25℃ has been constructed for the first time. There are five crystallization surfaces corresponding to the eutectic solutions saturated with NaCl and KCl, LiCl·H₂O, MgCl₂·6H₂O, Li-Carnallite and K-Carnallite respectively;the monovariant lines. P₃T₁(corresponding to NaCl+ KCl+ K-Carnallite), E₅T₁(NaCl+ KCl+LiCl·H₂O ), E₄P(NaCl+K-Carnallite+MgCl₂·6H₂O), PT₂( NaCl+K-Carnallite+ Li-Carnallite), T₁T₂( NaCl+K-Carnallite+LiCl·H₂O), P₂P( NaCl+MgCl₂·6H₂O+Li-Carna-llite), E₃T₂(NaCl+Li-Carnallitc+LiCl·H₂O), E₁T₁( KCl+LiCl·H₂O+K-Car-nallitc), E₂T₂(LiCl·H₂O+Li-Carnallite+ K-Carnallite), P₁P( MgCl₂·6H₂O+ Li-Carnallite+K-Carnallite), respcctivoly; and three quinary invariant points: T₁, T₂, Pcorresponding to the solutions saturated with LiCl·H₂O+NaCl+KCl+ K-Carnallitc, LiCl·H₂O+NaCl+Li-Carnallite+ K-Carnallite and Nacl+ MgCl₂·6H₂O+Li-Carnallite+ K-Carnallite.The results of studying the isothermal evaporation of mixtures showed that there was not any metastable solid phase occurring in the system and the supersaturation phenomena were unconsidcred.