Qinghai-Tibet salt lakes are famous for enriching boron and lithium resources. Nevertheless, the chemical species of borate in the brine varies with the chemical type of salt lake. Among them, the existing borate forms in sulfate-type salt lake brine are the most complicated. Generally, the borates do not crystallize out from the brine during the whole evaporation process of brine but accumulate in the bischofite-saturated brine in different kinds of boron species, which are supersaturated with magnesium borates. This phenomenon may significantly impact the subsequent separation and extraction of lithium and magnesium salts. Therefore, the deep research on the chemical forms, species distribution, and their interactions in the salt lake brine is of great significance for the highly efficient development of salt lake resources. Compared with the classical Raman spectroscopy, the simplified Raman integrating sphere, designed based on the Raman scattering principle, can improve the exciting lights efficiency and the Raman scattering signal. It is characteristic of a strong Raman scattering signal, low detection limit, and high signal-to-noise ratio for the characterization of the borate structures, which favors the quantitative analysis of the chemical forms of the borate in the complicated brine system. Based on the above, this study aimed to investigate the chemical forms of borate in salt lake brine using the Raman integrating spheres. It also elucidated the changes of polyborate ions during the brine evaporation process. Secondly, the response surface method was used to explore the effects of the coexisting salts on the determination of B(OH)3 in salt lake brine. The results showed that borates in the salt lake brine could be polymerized to form poly borate ions such as B3O3(OH)-4 and B6O7(OH)2-7 during the brine evaporation process, which agreed well with the borate changes in the alkaline-earth metal solution system of MgCl2-MgO-2B2O3-H2O, but differed greatly with that changes in alkaline metal solutions. The relative error of the B(OH)3 determination in brine was less than 5% after being corrected by the response surface interference model. Therefore, the distribution of B(OH)3 in the brine was also studied during the evaporation process, which helped explain the polymerization mechanism among borate ions in brine from a quantitative perspective. In sum, this research could provide new ideas and methods for further study of borate speciation and their interaction mechanism in complicated brine systems.