Platinum film is an important part of thin-film platinum resistance temperature sensors. Due to its low mechanical strength, the formation of a layer of encapsulated glass on its surface is currently the main means of protecting the platinum film. BaO-Al2O3-SiO2 (BAS) system glass-ceramics is expected to be introduced into the field of thin-film platinum resistor encapsulation due to its advantages of good chemical stability, high mechanical strength, and high-temperature stability. The addition of nucleating agents to the glass components can promote the crystallization of the glass, and the nucleating agents have an important influence on the crystallization of the glass. Therefore, Li2O, ZrO2, TiO2 and Y2O3 were used as nucleating agents for BAS microcrystalline glass, and the effects of the types and contents of nucleating agents on the crystallization of microcrystalline glass were investigated. Research showed that the order of the strength of the promoting effect on glass crystallization behavior was Li2O>TiO2>Y2O3>ZrO2. Li2O significantly promoted the crystallization of the BAS glass, and with the increase of Li2O content, the orthorhombic barium silicate phase was firstly precipitated, and the hexagonal barium feldspar phase appeared next. With the increase of Li2O content, monoclinic barium silicate phase was firstly precipitated, followed by hexagonal barium feldspar phase, and finally barium silica. Secondly, when the Li2O molar fraction was 1.5%~2.5%, the glass expansion coefficient of the BAS system was (7.75~8.13)×10-6/℃, which matched with the platinum resistor substrate alumina ceramics (7.6×10-6/℃). Finally, the crystallization mechanism of BAS glass-ceramics was revealed: the addition of Li2O played the role of "accumulation" in the glass, seizing the O2- in the glass network structure, destroying the glass structure, reducing the degree of structural densification, thus lowering the glass transition temperature and the glass viscosity, accelerating the migration of SiO2, and facilitating the glass to precipitate crystals.