The solubility and metastable zone width of boric acid in the simulated oilfield brine system of NaCl-KCl-CaCl2-H2O were studied at low temperature by the turbidity method. The nucleation kinetic constant A and the interfacial energy gamma of boric acid were calculated with nucleation theory. Results showed that the solubility of boric acid in the simulated oilfield brine system was mainly determined by the coexisting salt of CaCl2 and decreased with increasing concentrations of CaCl2, even though the presence of NaCl and KCl has a salt-in effect on the solubility. However, the metastable zone width was affected by the three coexisting salts and it changes differently with the varied concentrations. The possible reason can be explained by the dependence of the interfacial energy gamma on the slat concentration. On the basis of the above results, the crystallization behavior of boric acid during oilfield brine evaporation was investigated for the first time. It was deeply affected by the coexisting salts in brine.