In this Letter, we report an ultraflat high-power supercontinuum (SC) based on a low-loss short-length fluorotellurite fiber. A novel high-peak power dual-Raman soliton femtosecond laser is used as a pump source, which effectively extends the mid-infrared SC spectral range and enhances the flatness of the SC. Finally, we obtained a 10.4 W SC laser source with a spectral range from 1.8 to 4.2 µm in a 34 µm fluorotellurite fiber; the 5 dB bandwidth of the source completely covers 1.9-4.05 µm. To the best of our knowledge, this is the first report of a high-power SC generated in a fluorotellurite fiber with a flat spectral edge of >4 µm. This result highlights the fluorotellurite fiber's spectral broadening capabilities under high-power conditions, demonstrating performance on par with that of ZBLAN fibers.