We investigate theoretically the high-order harmonic spectrum extension and numerical generation of an intense isolated attosecond pulse from He+ ion irradiated by a two-color laser field. Our simulation results show that the chirp of the fundamental field can control HHG cutoff position. Also, these results show that the envelope forms of two fields are important factors for controlling the resultant attosecond pulses. Besides, the effects of relative intensity are investigated. As a result, by using the optimized conditions an intense isolated 126-as (attosecond) pulse can be observed