The invention discloses a linear displacement detection device of a dual-redundancy rotary telescopic shaft. The linear displacement detection device converts rotary telescopic motion of the shaft into a linear motion, so as to perform linear displacement contact type detection on the shaft, the problem of inconvenient detection of linear displacement of the rotary telescopic shaft is solved, structures such as a connecting rod, a bearing and the like are skillfully utilized to realize functions, the structure is compact and reliable, and the linear displacement detection device provides technical support for the miniaturization of a transmission structure having a redundant function.