Abstract: This paper elucidates mainly how to extract the pitch signals from speech sounds and how to indicate the pitch inflections by curves, and discusses further the characteristics of the pitch curves in Standard Chinese. The "maximum peaks" of voiced sound wave forms are extracted by means of the nonlinear technique (with detector and differenciating circuit), and then transformed into sawtoothed waves. The pitch inflections of speech sounds are indicated by the curves, which are drawn to enclose the ends of amplitudes of the sawtoothed waves. Generally speaking, the pitch curves of the syllables in Standard Chinese could be divided into three parts, namely:"the onset-curving section", "the tone section", and "the end-falling section". Since the pitch inflections of the "tone sections" in the four tones always bear their distinctive patterns (i.e., the first tone is high-level, the second-middle-rising, the third-low-falling-rising, and the fourth-high-falling), only the pitch pattern of the "tone section" plays a distinctive part of the tone in Standard Chinese.