Word Complexity Measure (WCM, Stoel-Gammon, 2010) is a system of phonological assessment for children's speech productions, a method that focuses on the complexity rather than accuracy. With its flexible parameter program, the assessment can be adjusted to the phonological properties of different languages. In the current study, the WCM was used to assess speech production of three Mandarin-learning children from birth to three years old. In addition to the original parameters in Stoel-Gammon (2010), the Chinese version of WCM made some adjustments, including incorporating productions of fricatives, affricates, /z/, /y/, and the late acquired vowels and consonants, to examine the complexity of speech productions. Major findings in the developmental changes of the first 3 years are: 1) the complexity of the intelligible words increased, with individual differences in the stability of changes; 2) the complexity of the unintelligible syllables also elaborated; 3) the percentage of simple words/syllables decreased in both intelligible and unintelligible productions.