Solubilities and properties (density, conductivity and pH value) of solutions in the quaternary system Li^+ ,K^+//CO3^2-,B4O7^2-—H2O at 288K were experimentally studied with the isothermal equilibrium method. The phase diagram of the system consisted of two invariant points E and F, five univariant curves, and four crystallization fields that belonged to K2CO3·3/2H2O, Li2B4O7·3H2O,K2B4O7·4H2O and Li2CO3, The composition of the solution corresponding to E was ω(CO3^2-)=2.27%, ω(B4O7^2-)=6.05%,ω(K^+)=4.30%, ω(Li^+)=0.30% and the equilibrium solids were Li2B4O7·3H2O+K2B4O7·4HeO+Li2CO3;The composition of the solution for F was ω(CO3^2-)=22.45%, ω(B4O7^2-)=1.88%, ω(K^+)=29.96%, ω(Li^+)=0.03% and the equilibrium solids were K2CO3·3/2H2O+K2B4O7·4H2O+Li2CO3,K2CO3 possesses strong salting-out effect on K2B4O7,Li2CO3 and Li2B4O7.