Word spurt is characterized by a sudden rise of vocabulary growth toward the end of one-word stage, typically around one and a half years old, when the child has a vocabulary of about 50 words. Many researchers have reported vocabulary spurt in early lexical development according to parental reports as well as longitudinal case studies. Previous studies usually analyze word spurt from a single language or non-language perspective, and there is no systematic investigation of children’s linguistic features around word-spurt. In Chinese, a few studies focus on the early lexical growth, the distribution of early lexical categories and the using frequency of early vocabulary, which also have not provided sufficient information to probe into the characteristics of early lexical, syntactic and semantic development around word-spurt time. Based on the longitudinal data of five Mandarin-speaking children, this paper explores word spurt in children’s early lexical, syntactic and semantic development. The data on early lexical development showed that for five children, a sudden increase in vocabulary was witnessed at 18 months. Children’s naming insight was the foundation for the achievement of a capability to handle grammatical relations, as these results confirmed a close link between the onset of word combinations and word spurt in terms of relative chronology. The two-word stage symbolizing the occurrence of early syntax began for the children around 17 months, almost the same time with word spurt. A longitudinal study on early semantic development showed that the acquisition of meanings for five kids was a quick process. Children’s first overextension occurred at 9 months, and overextension was highly restrained before 16 months. Then, overextended words reached the highest number around 18 months, petering out gradually until the end of the second year. On the whole, less than 7% of the children’s vocabulary was overextended. In addition, basic-level words constituted almost all the early common nouns, which displayed the conceptual primacy of basic-level words in early lexical development. The elaboration of noun hierarchies consisted mainly in the addition of subordinate-level words, with the first appearing at 17 months. The gradual disappearance of overextensions and the addition of subordinate-level words around word spurt implied a change of word-referent abilities during this period. After that, there was a great improvement of children’s word-referent mapping abilities. In sum, it appeared that 18 months was a milestone for children’s early lexical, syntactic and semantic development. It was around this time that children displayed a series of great changes: a rapid growth of vocabulary; an occurrence of word combinations; a gradual disappearance of overextended words and a gradual increase of subordinate-level words. Word spurt marks not only a quantitative change of vocabulary, but also a qualitative change in children’s whole language system.