The invention discloses a railway sleeper replacing device and an operation method of the railway sleeper replacing device. The railway sleeper replacing device is installed on an excavator and used for sleeper replacement and comprises an installation seat, a ballast excavation plate installed in front of the installation seat and used for railway ballast excavation and backfill, a horizontal rotation mechanism installed below the installation seat, a vertical turnover mechanism installed below the horizontal rotation mechanism, and sleeper clamping mechanisms installed at the two axial endsof the vertical turnover mechanism and used for clamping and releasing a sleeper. The technical problems that track spikes are likely to collide with steel rails and the automation degree and construction operation efficiency are low by the adoption of an existing sleeper replacing mode can be solved.