The invention relates to a multi-range acquisition unit, and a medium voltage switch cabinet signal acquisition device and system. The multi-range acquisition unit comprises a first follower module, an amplifier module, an A/D module and a processor for sending sampling information to a protection and monitoring device. Input ends of the first follower module and the amplifier module are used to receive the same current sampling signal. An output end of the first follower module is connected to a first A/D channel of the A/D module. An output end of the amplifier module is connected to a second A/D channel and a third A/D channel of the A/D module. Each A/D channel of the A/D module is connected to the processor. The processor is also connected to a gain control end of the third A/D channel to control the signal gain of the third A/D channel. According to the invention, the multi-channel sampling signals can be controlled through operational amplifiers and controllable A/D channel gains, different current channel data are selected for protection or measurement calculations, and protection and measurement requirements can be met simultaneously.