We investigate the generation of isolated broadband attosecond pulses for a model of He atom driven by a midinfrared (MIR) laser pulse in combination with a ultraviolet (UV) controlling pulse. By solving the time-dependent Schrdinger equation with split-operator method,the high-order harmonic and attosecond pulse are obtained with MIR and UV pulses,whose wavelengths are 1400 nm and 78 nm respectively. By adjusting the time delay of two lasers,we can enhance the contribution of one electron trajectory and suppress the other electron trajectory. Thus we obtain a shorter isolated attosecond pulse,compared with the pulse produced by the He atom driven by the infrared and ultraviolet fields.