We propose a theoretical scheme to generate a broadband supercontinuum using a modulated chirped polarization gating technique. By this technique, a broadband continuum of 155 eV can be obtained at microscopic level. The modulations on the supercontinuum can be eliminated after propagation. Then a smooth broadband supercontinuum with the bandwidth of 155 eV can be generated. As a result, isolated sub-100-attosecond pulses with tunable central wavelengths could be obtained straightforwardly. Our simulations also reveal that an isolated attosecond pulse can still be generated by using multicycle driving laser pulses, and the central wavelength of isolated attosecond pulse can be controlled by adjusting the delay τd (τd is the delay of the two counter-rotating circularly polarized pulses.). We propose a theoretical scheme to generate a broadband supercontinuum using a modulated chirped polarization gating technique. By this technique, a broadband continuum of 155 eV can obtained at microscopic level. The modulations on the supercontinuum can be eliminated after propagation. Then a smooth broadband As a result, isolated sub-100-attosecond pulses with tunable central forwards could be obtained straightforwardly. Our simulations also reveal that an isolated attosecondcond pulses can still be generated by using multicycle driving laser pulses , and the central wavelength of isolated attosecond pulse can be controlled by adjusting the delay τd (τd is the delay of the two counter-rotating circularly polarized pulses.).