Molybdenum disulfide (MoS₂), as a kind of two-dimensional(2D) material with novel physical properties and excellent electrical performances, has great potential applications in electronic devices. Efficient and controllable growth of large-size single crystal MoS₂ is a major difficulty that must be overcome towards scalable production. Chemical vapor deposition (CVD) is considered as the most promising means for industrial production of 2D materials. Here in this work, the high-quality and millimeter-level single crystal MoS₂monolayer grows on molten glass by the pre-chemical vapor deposition, in which MoO₃ film deposited on the molten glass is used as Mo precursor instead of MoO₃ powder. In addition, by introducing WO₃ powder into such a CVD system, MoS₂-WS₂ lateral heterojunctions can also be obtained. Raman and PL measurements indicate that the as-grown MoS₂ monolayer samples possess high quality. The Back-gate FETs are fabricated on SiO₂/Si substrates by using transferring elelctrode methods to investigate the electrical properties of the as-grown MoS₂ crystals. At room temperature and atmosphere pressure, the on-off ratio can reach 10⁵ and the carrier mobility can arrive at 4.53 cm²/(V·s). The low-cost and high-quality large-size material growth method pave the way for the scalable production of such a 2D material based electronic devices.