The invention discloses a novel gear selecting and shifting mechanism assembly for a speed changer. The novel gear selecting and shifting mechanism assembly comprises a small cover assembly and a shifting fork shaft assembly, wherein the small cover assembly comprises a self-locking mechanism, an interlocking mechanism and a neutral gear and reverse gear signal selecting device; six gear shifting positions are set in the shifting fork shaft assembly; the self-locking mechanism consists of a self-locking pin shaft and a fan-shaped self-locking block; the interlocking mechanism consists of a fork-shaped interlocking fork; the small cover assembly comprises a small cover shell, a gear shifting shaft, a sensor driving ring, a driving pin, a fan-shaped self-locking block, a gear shifting head, a centering base ring, a distance ring, a centering spring, the self-locking pin shaft and the interlocking fork; the shifting fork shaft assembly comprises a shifting fork shaft, a shifting block, a shifting fork and a friction plate; the friction plate is arranged in a fork pin of the shifting fork and is compressed with the surface of the shifting fork tightly; and a synchronizer sliding disc is arranged in a fork pin groove of the shifting fork. Compared with the prior art, the novel gear selecting and shifting mechanism assembly has the advantage that in the gear shifting process, a friction material can buffer impact when the synchronizer sliding disc is shifted by the shifting fork, so that gears is shifted stably.