The invention relates to a multichannel slit rotating switching device for a multi-target optical fiber spectrometer, and the device consists of an incident slit, an optical fiber, a slit switching system and a slit positioning clamping system. The device is characterized in that the incident slit, a slit rotating switching mechanism and the optical fiber are installed on a slit substrate; the slit substrate is connected to a supporting seat through a pre-tightening steel belt; the optical fiber is installed on the slit substrate; a slit substrate connecting seat is fixed on the slit substrate, and a positioning hole, fixed at the upper end of the slit, of the slit substrate connecting seat is coincided with a positioning hole of a rotating positioning seat, and cooperates with the positioning hole of the rotating positioning seat through a high-precision bearing; the slit and the slit substrate connecting seat are connected through a slit rotating positioning block; the slit rotatingpositioning block cooperates with the slit through high-precision processing; a corresponding number of spherical positioning mechanisms is disposed between the slit rotating positioning block and theslit according to the number of slits. The device is convenient for installation, disassembly and debugging, does not have any obstruction, employs positioning and clamping mechanisms, is provided with a pre-tightening positioning ring, is stable in switching, and is high in precision.