The invention discloses a straight bevel gear transmission mechanism with different rotating speeds of forward rotation and reverse rotation, and belongs to the field of reducers. The problems that anexisting straight bevel gear reducer is complex in structure and high in cost are solved. The straight bevel gear transmission mechanism comprises an input shaft, an output shaft, a shifting fork shaft and a shifting fork, and further comprises a first straight bevel gear pair and a second straight bevel gear pair. The first straight bevel gear pair comprises a first active bevel gear and a firstpassive bevel gear, and the second straight bevel gear pair comprises a second active bevel gear and a second passive bevel gear. The first active bevel gear and the second active bevel gear are arranged on the input shaft and can axially slide; the first passive bevel gear and the second passive bevel gear are arranged on the output shaft; and two fork feet of the shifting fork are connected with the first active bevel gear and the second active bevel gear correspondingly. Under the premise that the straight bevel gear reducer can achieve the different rotating speeds of forward rotation andreverse rotation, the gear transmission mechanism is simplified, and the production cost of the straight bevel gear reducer with the different rotating speeds of forward rotation and reverse rotationis lowered.