The invention discloses a gear shift mechanism of a six-speed automobile speed changer, which belongs to the technical field of the operating device for an automobile mechanical speed changer. The gear shift mechanism comprises a forked axle assembly, an interlocking and self-locking mechanism and a top cover assembly, wherein, the forked axle assembly comprises a forked axle with fours gears of 1, 2 3, and 4, a forked axle with two gears of 5 and 6 and a reverse gear forked axle; the interlocking and self-locking mechanism comprises an interlocking plate, a self-locking assembly, a self-locking spring and a self-locking steel ball; and the top cover assembly is assembled above the shell of the speed changer, and the top cover assembly comprises a gear selection shaft, a gear-selection shifting head, a gear shift shaft and a gear shift shifting head. Compared with the prior art, the six-speed automobile speed changer has the advantages of reasonable design, simple structure, low production cost, convenient manufacture and portable operating device for gear selection and shift.