A hundred-watt-level spatial mode switchable all-fiber laser is demonstrated based on a master oscillator power amplifier scheme. The performance of the amplifier with two seed lasers, i.e., with the acoustically induced fiber grating (AIFG) mode converter inside and outside the seed laser cavity, is investigated. Real-time mode switching with millisecond scale switching time between the LP01 and LP11 modes while operating in full power (>100W) is realized through an AIFG driven by radio frequency modulation. This work could provide a good reference for realizing high-power agile mode switchable fiber lasers for practical applications.