We theoretically investigate the process of the efficient ultra-broadband supercontinuum generation in the mid-infrared polarization gating. The polarization gating at 2000 nm is adopted to restrict the recombination of the electron into one-half optical cycle and extend the spectrum cut-off to 270 eV. And a 0.5 fs ultraviolet pulse is synthesized to the polarization gating to control the ionization process. Then the harmonic intensity is enhanced by 4—5 orders, and a 240eV supercontinuum is obtained, supporting a 16 as pulse generation. By filtering out different ranges of the supercontinuum, isolated 110 as pulses with tunable central wavelengths are efficiently generated.