Language and pronunciation acquisition for infants and children is a gradual process which is influenced by numerous factors, such as physiological, psychological, and environmental ones. Among all these factors, the physiological factor impose the most direct impact. The maturation process of the infant's vocal organs affected their language acquisition order, with different vocal organs generating different impacts. Based on the study of speech of an infant from birth to two-year-old, this paper links acoustic analysis with developmental of vocal organs, vocal track, tongue and lips in particular, and indicates that during the pronunciation acquisition of the infant during this period, development of vocal track mainly affects their pitch of voice. While, lips and the tongue as articulators, mainly affects pronunciation acquisition sequence.