The invention relates to an installation system and method for rotary encoder redundancy detection. The installation system includes a main gear, a slave gear, a first U-shaped installing plate and a second U-shaped installing plate, wherein the main gear sleeves an encoder installing shaft, and the main gear is fixedly installed on the first U-shaped installing plate; the slave gear sleeves a slave gear shaft, and is fixedly installed on the second U-shaped installing plate; and the slave gear is connected with the main gear in a meshed mode. When the installation system is used, a main encoder is used for detecting the operating data of the encoder installing shaft; the encoder installing shaft drives the main gear to rotate, the main gear drives the slave gear to rotate, the slave gear drives the slave gear shaft to rotate, a slave encoder is arranged on the slave gear shaft, and the slave encoder indirectly detects the operating data of the encoder installing shaft. When a fault occurs in the main encoder, data detected by the slave encoder are utilized to participate in automated control, production is not influenced due to maintenance of the main encoder, and thus production efficiency is greatly improved.