The invention discloses a novel pitch-varying silent chain which is obtained by modifying working chain plate holes and roll pin contours of the pitch-varying silent chain. The novel pitch-varying silent chain is mainly composed of a plurality of groups of working chain plates, short roll pins, long roll pins and guide pieces. The short roll pins and the long roll pins penetrate through the chain plate holes of the working chain plates to enable the plurality of groups of working chain plates to be connected in a head-to-tail mode, and the guide pieces enable exposed portions located at two ends of two adjacent long roll pins to be fixed. A chain plate hole contour line of the working chain plates is formed by a section of chain-plate heart-shaped contour line, three sections of chain-plate arc-shaped contour lines and two sections of chain-plate straight-line contour lines. A contour line of the short roll pins is formed by two sections of symmetric roll pin involutes, one section of roll-pin heart-shaped contour line and four sections of roll-pin arc-shaped contour lines. A contour line of the long roll pins, the contour line of the short roll pins and a contour line of guide piece holes are the same. The novel pitch-varying silent chain is characterized by varying pitch, the polygon effect, impact and vibration of the pitch-varying silent chain transmission can be remarkably reduced, the abrasion and the noise are reduced, and fatigue durability of the silent chain is improved.